Data slicer, data slicing method, and amplitude evaluation value setting method

ABSTRACT

A data slicer  300  includes a slice level calculation unit  310  that determines whether a detected digital video signal is a CRI signal on the basis of the amplitude of the signal, and sets a reference slice level and upper and lower slice levels which are obtained by providing offset in the reference slice level, by using only the CRI signal; a data slicing unit  160  that binarizes a digital video signal S 140  using the slice levels; a decoding circuit  170  that converts binarized serial data into parallel data; and a data selection unit  320  that selects data including no error from the decoded data, and outputs the selected data through a video signal output terminal  190 . Therefore, even when the video signal is distorted, this data slicer can set appropriate slice level data to binarize the video signal, thereby suppressing the occurrence rate of decoding errors.

FIELD OF THE INVENTION

[0001] The present invention relates to a data slicer, a data slicingmethod, and an amplitude evaluation value setting method and, moreparticularly, to a data slicer, a data slicing method, and an amplitudeevaluation value setting method for calculating a slice level thatenables to binarize a video signal into a proper value.

BACKGROUND OF THE INVENTION

[0002] As a method for transmitting data utilizing serial transmission,there is a character broadcast system by which character broadcast dataare transmitted in vertical blanking intervals of video signals.

[0003] There are various kinds of character broadcast systems thatemploy different superimposition lines upon which character broadcastdata (character broadcast serial data) are superimposed, or transmissionclocks of different frequencies, and various kinds of analog videosignals on which the character broadcast serial data are superimposedare transmitted at present in various regions over the world.

[0004] Acharacter broadcast analog video signal (see S140 in FIG. 11) isa signal including a horizontal sync signal A that indicates start of ahorizontal blanking interval, a color burst signal B for colorreproduction, a clock run-in (hereinafter, referred to as CRI) signal Cthat is a reference waveform and employed to set a slice level forbinarizing a signal, a framing code signal D that indicates thecharacter broadcast type, and a text data signal E including characterbroadcast data to be transmitted. Hereinafter, a period in which theslice level is set on the basis of the CRI signal C is referred to as aCRI detection period, a period in which the frame code signal D isreceived is referred to as a framing code period, and a period in whichthe text data signal E is received is referred to as a text data period.

[0005] The data unit of the character broadcast serial data is composedof 8 bits, and one bit among these 8 bits is a parity bit that is addedto detect the presence or absence of decoding errors. The characterbroadcast system employs a method by which the presence or absence ofdecoding errors is checked on the basis of whether or not an odd numberof “1” are included in each unit of decoded data, and accordingly dataof 8 bits which include an odd number of “1” are transmitted. Thus, whenactual data includes only an even number of “1”, the parity bit is setat “1”, so that each data unit includes an even number of “1”.

[0006] When characters that are superimposed upon such an analog videosignal are to be displayed, the received analog video signal isinitially binarized by a data slicer to extract character broadcast datain accordance with a transmission clock, thereby extracting characterbroadcast serial data.

[0007] Hereinafter, the construction and operation of the conventionaldata slicer will be described with reference to FIG. 10.

[0008] As shown in FIG. 10, the conventional data slicer 500 includes anA/D converter 120 for converting an analog videosignal S110 inputtedthrough a video signal input terminal 110, upon which characterbroadcast serial data are superimposed, into a digital video signalS120; a CRI detection unit 130 for generating a CRI detection rangesignal S132 that indicates a CRI detection period on the basis of thedigital video signal S120; a low-pass filter (hereinafter, referred toas LPF) 140 that eliminates noises from the digital video signal S120and outputs a digital video signal S140; a slice level calculation unit510 that sets a slice level on the basis of the digital video signalS140 which is inputted during the CRI detection period; a data slicingunit 220 that binarizes the digital video signal S140, using the slicelevel that is set by the slice level calculation unit 510; and adecoding circuit 230 that converts the binarized serial data intoparallel data to perform a decoding process, and outputs decoded dataS230 to outside the data slicer 500 through a video signal outputterminal 190.

[0009] The CRI detection unit 130 includes a sync separation circuit 131that separates a vertical sync signal S131 a and a horizontal syncsignal S131 b from the digital video signal S120; and a CRI detectionrange signal generation circuit 132 that outputs a CRI detection rangesignal S132 that indicates a predetermined line and position as adetection period for a CRI signal C, on the basis of the vertical syncsignal S131 a and the horizontal sync signal S131 b.

[0010] The slice level calculation unit 510 includes a falling detectioncircuit 151 that outputs a falling detection pulse S151 when detecting afalling of the digital video signal S140 in the CRI detection period; afrequency calculation circuit 152 that calculates the frequency of thedigital video signal S140 on the basis of the falling detection pulseS151, and outputs frequency data S152; a frequency evaluation circuit153 that compares the frequency data S152 with previously-held frequencydata of a CRI signal C for the character broadcast system, and outputs afrequency evaluation gate pulse S153 during a period in which thefrequency data S152 corresponding to a predetermined character broadcastsystem are outputted; and a CRI evaluation circuit 154 that extracts apulse corresponding to a falling of the predetermined characterbroadcast system from the fall detection pulse S151, and outputs afrequency evaluation pulse S154. The slice level calculation unit 510further includes a maximum/minimum retrieval circuit 155 that retrievesthe maximum and minimum values of the amplitude of the digital videosignal S140 during the CRI detection period, and outputs maximum valueretrieval data S155 a and minimum value retrieval data S155 b; and anaverage calculation circuit 511 calculating the average amplitude of thedigital video signal S140 on the basis of the maximum value retrievaldata S155 a and the minimum value retrieval data S155 b, with employingthe frequency evaluation pulse S154 as a load pulse, and outputs thecalculated average as slice level data S511 to the data slicing unit220.

[0011] The data slicing unit 220 includes a binarization circuit 221that performs threshold evaluation using the slice level data S511(i.e., determines whether the digital video signal S140 is larger orsmaller than the slice level data S511) to binarize the digital videosignal S140, and outputs binarized data S221 to an extraction circuit222; and an extraction circuit 222 that extracts character broadcastserial data from the binarized data S221 in timing of an extractionpulse S162 that is generated by an extraction pulse generation circuit162, and outputs extracted serial data S222.

[0012] Next, the operation of the conventional data slicer 500 that isconstructed as described above will be described with reference tofigures.

[0013] A timing chart that illustrates the operation of the conventionaldata slicer 500 is shown in FIG. 11. In FIG. 11, the same orcorresponding elements as those in FIG. 10 are denoted by the samereference numerals. Further, reference character A denotes a horizontalsync signal, B denotes a color burst signal, C denotes a CRI signal, Ddenotes a framing code signal, E denotes a text data signal, and T31 toT36 denote times when signals included in the digital video signal S140vary.

[0014] When an analog video signal S110 upon which character broadcastserial data are superimposed is inputted through the video signal inputterminal 110, the A/D converter 120 samples the analog video signal S110using a sampling clock fs (MHz) to convert the same into a digitalsignal, and outputs the digital video signal S120 to the CRI detectionunit 130 and the LPF 140. Then, the LPF 140 eliminates noises from thedigital video signal S120, and outputs a resultant digital video signalS140 to the slice level calculation unit 510 and the data slicing unit220. FIG. 11 shows an example of the digital video signal S140 that isobtained by A/D-converting the analog video signal S110 and eliminatingnoises therefrom. In this FIG. 11, black dots show the digital videosignal S120 (S140) which is obtained by sampling the analog video signalS110 using the sampling clock fs.

[0015] At time T31, the digital video signal S120 including a horizontalsync signal A and a vertical sync signal is inputted to the CRIdetection unit 130. Then, the sync separation circuit 131 separates avertical sync signal S131 a and a horizontal sync signal S131 b from thedigital video signal S120.

[0016] Next, the CRI detection range signal generation circuit 132obtains a start position (time T32) and an end position of the CRIsignal C on the basis of the vertical sync signal S131 a and thehorizontal sync signal S131 b, and outputs a CRI detection range signalS132 to the fall detection circuit 151 and the maximum/minimum retrievalcircuit 155 during the CRI detection period.

[0017] During a predetermined time period in the period while the CRIdetection range signal S132 is outputted, the digital video signal S140including the CRI signal C is inputted to the slice level calculationunit 510, and then the slice level calculation unit 510 performs a slicelevel calculation process on the basis of the inputted CRI signal C. Tocalculate the slice level, the falling detection circuit 151 retrievesfallings of the digital video signal S140, and the maximum/minimumretrieval circuit 155 retrieves the maximum and minimum values of thedigital video signal S140, and outputs maximum value retrieval data S155a and minimum value retrieval data S155 b.

[0018] At time T33, the falling detection circuit 151 detects a firstfalling of the CRI signal C, and outputs a falling detection pulse S151to the frequency calculation circuit 152 and the CRI evaluation circuit154. At time T34, the falling detection circuit 151 detects the secondfalling of the CRI signal C, and outputs the falling detection pulseS151 to the frequency calculation circuit 152 and the CRI evaluationcircuit 154.

[0019] Then, the frequency calculation circuit 152 calculates thefrequency of the CRI signal C from the falling detection pulses S151which are detected at times T33 and T34, and outputs frequency data S152to the frequency evaluation circuit 153. On the basis of the frequencydata S15, the frequency evaluation circuit 153 determines whether thefalling that is detected by the falling detection circuit 151corresponds to a signal that is compliant with the predeterminedcharacter broadcast system or not. For example, when a falling due tonoises is detected, the frequency data S152 is different from thefrequency of the character broadcast system, and thus the frequencyevaluation circuit 153 determines that this is frequency data which isnot compliant with the predetermined character broadcast system. Whenthe frequency data S152 is the frequency of the predetermined characterbroadcast system, the frequency evaluation circuit 153 outputs thefrequency evaluation gate pulse S153 to the CRI evaluation circuit 154.

[0020] Then, on the basis of the frequency evaluation gate pulse S153,the CRI evaluation circuit 154 determines whether the falling detectionpulse S151 is a pulse that is compliant with the character broadcastsystem or not. The falling detection pulse S151 during a period in whichthe frequency evaluation gate pulse S153 is outputted is a pulse that iscompliant with the character broadcast CRI signal C, and the CRIevaluation circuit 154 extracts the corresponding pulse and outputs thefrequency evaluation pulse S154 to the average calculation circuit 511.

[0021] The average calculation circuit 511 samples the maximum valueretrieval data S155 a and the minimum value retrieval data S155 b, withutilizing the frequency evaluation pulse S154 as a load pulse, andcalculates the average value of the CRI signal C. Then, the averagecalculation circuit 511 outputs the calculated average value to the dataslicing unit 220 as slice level data S511. Here, a slice level SLV10which is set on the basis of the slice level data S511 is an appropriateslice level that can be employed when the framing code signal D and thetext data signal E are binarized after time T35.

[0022] When the digital video signal S140 including the framing codesignal D is inputted to the data slicing unit 220 at time T35, thebinarization circuit 221 determines whether the digital video signalS140 is higher or lower than the slice level data S511 to binarize thesignal into “0” or “1”, thereby generating binarized data S221. Then,the extraction circuit 222 extracts character broadcast serial data fromthe binarized data S221, in accordance with an extraction pulse S162that is outputted from the extraction pulse generation circuit 162, andoutputs extracted serial data S222. The decoding circuit 230 convertsthe extracted serial data S222 into parallel data, and obtains a framingcode.

[0023] When the digital video signal S140 including a text data signal Eis inputted to the data slicing unit 220 at time T36, the binarizationcircuit 221 binarizes the digital video signal S140 using the slicelevel data S511, to generate binarized data S221, like in the caseincluding the framing code signal D. Then, the extraction circuit 222extracts character broadcast serial data from the binarized data S211 inaccordance with the extraction pulse S612, and outputs the extractedserial data S222 to the decoding circuit 230. The decoding circuit 230converts the extracted serial data S22 into parallel data, then carriesout a decoding process depending on the type of the character broadcast,which is indicated by the framing code, and outputs decoded data S230through the video signal output terminal 190.

[0024] The decoded data that are outputted from the video signal outputterminal 190 are transferred to a display circuit (not shown), anddisplayed as characters.

[0025] However, the analog video signal S110 that is inputted from thevideo signal input terminal 110 may include distortion resulting fromgroup delay or reduction in electric field strength in a transmissionsystem. The conventional data slicer is adversely affected by noises dueto the distortion, and accordingly, when the analog video signal S140 isdistorted, the accuracy of the slice level data S511 that is calculatedby the slice level calculation unit 510 is lowered, whereby anappropriate slice level data S511 cannot be obtained.

[0026] Consequently, the binarization circuit 211 binarizes the digitalvideo signal S140 into an incorrect value, so that the occurrence rateof decoding errors gets higher at the decoding process for the binarizeddata S211.

[0027] Hereinafter, a description will be given of the operation of theconventional data slicer 500 in a case where a distorted analog videosignal S110 is inputted thereto, with reference to the drawings.

[0028]FIG. 12 shows the operation of the conventional data slicer 500 inthe case where an analog video signal S110 that is distorted due togroup delay or reduction in the electric field strength is inputtedthereto. In FIG. 12, the same or corresponding elements as those in FIG.11 are denoted by the same reference numerals. Reference characters T41to T46 denote times when signals included in the digital video signalvary.

[0029] When the analog video signal S110 is inputted through the videosignal input terminal 110, the A/D converter 120 converts the analogvideo signal S110 into a digital signal, and outputs the digital videosignal S120 to the CRI detection unit 130 and the LPF 140. Then, the LPF140 eliminates noises from the digital video signal S120, and outputs aresultant digital video signal S140 to the slice level calculation unit510 and the data slicing unit 220. FIG. 12 shows an example of thedigital video signal S140 that is obtained by A/D-converting thedistorted analog video signal S110 and eliminating noises from theconverted signal.

[0030] Further, reference character C′ denotes noises which occur duringa period in which the CRI detection range signal S132 is outputted, andcannot be eliminated by the LPF 140. The reason why the digital videosignal S140 is distorted even when the noise elimination is performed bythe LPF 140 is that this video signal is affected by noises that cannotbe eliminated even by the LPF 140. Further, black dots in FIG. 12 showthe digital video signal S120 (S140) which is obtained by sampling theanalog video signal S110 using the sampling clock fs.

[0031] At time T41, the digital video signal S120 including a horizontalsync signal A and a vertical sync signal is inputted to the CRIdetection unit 130, and then the sync separation circuit S131 separatesthe vertical sync signal S131 a and the horizontal sync signal S131 bfrom the digital video signal S120.

[0032] At time T42, the CRI detection range signal generation circuit132 obtains a start position and an end position of the CRI signal C onthe basis of a vertical sync signal S131 a and a horizontal sync signalS131 b, and outputs a CRI detection range signal S132 during the CRIdetection period.

[0033] While the CRI detection range signal generation circuit 132 isoutputting the CRI detection range signal S132, the slice levelcalculation unit 510 calculates a slice level on the basis of the CRIsignal C. While the CRI detection range signal S132 is being inputted tothe slice level calculation unit 510, the falling detection circuit 151retrieves a falling of the digital video signal S140, and themaximum/minimum retrieval circuit 155 retrieves the maximum and minimumvalues of the digital video signal 140.

[0034] At time T43, the falling detection circuit 151 erroneouslydetects a falling of the noises C′ in the digital video signal S140 as afalling of the CRI signal C, and generates a falling detection pulseS151. Also at time T44, the falling detection circuit 155 erroneouslydetects a falling of the noise C′ in the digital video signal S140 as afalling of the CRI signal C, and generates a falling detection pulseS151.

[0035] Then, the frequency calculation circuit 152 calculates thefrequency of the digital video signal S140 on the basis of the fallingdetection pulses that are detected at time T43 and T44, and outputfrequency data S152. On the basis of the calculated frequency data S152,the frequency evaluation circuit 153 determines whether the failingsthat are detected by the falling detection circuit 151 correspond to asignal that is compliant with the predetermined character broadcastsystem or not. When the interval between failings of noises C′ is equalto the interval between failings of the CRI signal C, like the digitalvideo signal S140 shown in FIG. 12, the frequency evaluation circuit 153erroneously determines that the frequency of the noises C′ is afrequency that is compliant with the predetermined character broadcastsystem, and outputs the frequency evaluation gate pulse S153 to the CRIevaluation circuit 154. Further, on the basis of the frequencyevaluation gate pulse S153, the CRI evaluation circuit 154 erroneouslydetermines that the falling detection pulse S151 is a pulse which iscompliant with the character broadcast, and outputs a frequencyevaluation pulse S154.

[0036] The average calculation circuit 511 samples the maximum valueretrieval data S155 a and the minimum value retrieval data S155 b, usingthe frequency evaluation pulse S154 as a load pulse, and calculates theaverage value of the noise C′ in the CRI signal C. Then, the averagecalculation circuit outputs the calculated average to the data slicingunit 220 as slice level data S511. A slice level SLV11 that is set onthe basis of the slice level data S511 calculated using the noise C′ islower than the slice level SLV10 that is set using the CRI signal Cincluding no distortion.

[0037] At times T45 and T46, the CRI signal C is detected. The fallingdetection circuit 151 detects the first falling of the CRI signal C attime T45, then detects the second falling of the CRI signal C at timeT46, and outputs falling detection pulses S151. The maximum/minimumretrieval circuit 155 retrieves the maximum and minimum values of thedigital video signal S140, and outputs maximum value retrieval data S155a and minimum value retrieval data S155 b. In the digital video signalS140 shown in FIG. 12, the maximum value of the noises C′ is smallerthan the minimum value of the CRI signal C, so that the minimum valueretrieval data S155 b is not updated by the CRI signal C, and thus theminimum value of the noises C′ is continuously outputted.

[0038] As the frequency that is calculated by the frequency calculationcircuit 152 on the basis of the falling detection pulses that aredetected at times T45 and T46 is a frequency conforming to the characterbroadcast system, the frequency evaluation pulse S154 is inputted to theaverage calculation circuit 511. The average calculation circuit 511samples the maximum value retrieval data S155 a and the minimum valueretrieval data S155 b using the frequency evaluation pulse S154 as aload pulse, and calculates the average value of the digital video signalS140. Then, the average calculation circuit outputs the calculatedaverage to the data slicing unit 220 as slice level data S511.

[0039] However, since the minimum value retrieval data S155 b is theminimum value of the noise C′, a slice level SLV12 that is set on thebasis of the slice level data S511 is improperly lower than anappropriate level. Consequently, the binarization circuit 211 performsbinarization using the slice level data that is lower than theappropriate level, so that it may binarize the framing code signal D andthe text data signal E into improper values. Accordingly, when extractedserial data S222 that are extracted from binarized data S221 inaccordance with an extraction pulse S162 are decoded by the decodingcircuit 230, decoding errors may occur.

[0040] Further, as the slice level calculation is performed only in theCRI detection period, improper slice level data are obtained when theshape of the digital video signal S140 varies after the CRI signal C.Consequently, the binarization circuit 221 binarizes the signal into animproper value, whereby the probability of occurrence of decoding errorsis increased.

[0041] Further, when a waveform equalization filter is used to correctdistortion of the waveform in the transmission system, the circuit scaleis so large that the circuit scale of the data slicer is adverselyincreased.

SUMMARY OF THE INVENTION

[0042] The present invention has for its object to provide a dataslicer, a data slicing method, and an amplitude evaluation value settingmethod, which can suppresses the occurrence rate of decoding errors evenwhen distortion occurs in a digital video signal due to group delay orreduction in the electric field strength in the transmission system.

[0043] Other objects and advantages of the invention will becomeapparent from the detailed description that follows. The detaileddescription and specific embodiments described are provided only forillustration since various additions and modifications within the spiritand scope of the invention will be apparent to those of skill in the artfrom the detailed description.

[0044] According to a 1st aspect of the present invention, there isprovided a data slicer comprising: an A/D conversion unit for convertingan input signal including data which are transmitted in serial, into adigital signal; a slice level data calculation unit for calculatingplural pieces of slice level data for binarizing the digital signal, onthe basis of the digital signal; a binarization unit for binarizing thedigital signal using the plural pieces of slice level data, to beconverted into plural binarized signals; an extraction pulse generationunit for generating an extraction pulse to be used for extracting thedata from the binarized signals; an extraction unit for extracting thedata from the binarized signals in accordance with the extraction pulse,thereby generating plural pieces of serial data; a decoding unit fordecoding the plural pieces of serial data, thereby generating pluralpieces of decoded data; and a decoded data selection unit forselectively outputting decoded data including no error, from among theplural pieces of decoded data. Therefore, a data signal can be binarizedinto a correct value using one of the plural pieces of the slice leveldata, and accordingly the data can be correctly extracted even whendistortion resulting from group delay or reduction in electric fieldstrength occurs in the data signal, thereby suppressing the occurrencerate of decoding errors.

[0045] According to a 2nd aspect of the present invention, in the dataslicer of the 1st aspect, the input signal is a signal having areference waveform of a predetermined cycle, and this data slicerincludes: a maximum/minimum retrieval unit for retrieving maximum andminimum values of the digital signal; and a reference cycle detectionunit for determining whether a cycle of the digital signal is the cycleof the reference waveform or not, and the slice level data calculationunit calculates the plural pieces of the slice level data, on the basisof an average value and an amplitude of the digital signal, which arecalculated from the maximum and minimum values when the referencewaveform cycle is detected. Therefore, the reference waveform isdetected on the basis of the cycle of the input signal, whereby theslice level data can be obtained by using the detected referencewaveform.

[0046] According to a 3rd aspect of the present invention, in the dataslicer of the 2nd aspect, the slice level data calculation unit employsthe calculated average value as reference slice level data, andcalculates upper slice level data by adding an offset value that isdecided on the basis of the calculated amplitude, to the reference slicelevel data, and lower slice level data by subtracting the offset valuefrom the reference slice level data. Therefore, the slice level dataaccording to the signal shape can be obtained.

[0047] According to a 4th aspect of the present invention, in the dataslicer of the 1st aspect, the input signal is a signal of characterbroadcast that is transmitted being superimposed upon a verticalblanking interval of a video signal. Therefore, the signal of characterbroadcast is binarized, and data included in the signal are extracted,whereby the received character broadcast signal can be displayed.

[0048] According to a 5th aspect of the present invention, there isprovided a data slicer comprising: an A/D conversion unit for convertingan input signal including a reference waveform of a predetermined cycleand amplitude, into a digital signal; a reference cycle detection unitfor determining whether a cycle of the digital signal is the cycle ofthe reference waveform or not; a maximum/minimum retrieval unit forretrieving maximum and minimum values of the digital signal; anamplitude evaluation unit for determining whether an amplitude of thedigital signal, which is calculated from the retrieved maximum andminimum values, is the amplitude of the reference waveform or not; aslice level data calculation unit that employs an average value of thedigital signal, which is calculated from the maximum and minimum valueswhen detecting the cycle and amplitude of the reference waveform, asslice level data; and a binarization unit for binarizing the digitalsignal into the slice level data, to be converted into a binarizedsignal. Therefore, by detecting the reference waveform on the basis ofthe amplitude, when noises having a cycle that is similar to that of thereference waveform are detected as the reference waveform, slice leveldata can be obtained only using the detected reference waveform, withexcepting the amplitude or average value obtained from the noises.

[0049] According to a 6th aspect of the present invention, in the dataslicer of the 5th aspect, the maximum/minimum retrieval unit retrievesmaximum and minimum values of the digital signal in each cycle, and theamplitude evaluation unit determines whether the amplitude calculatedfrom the maximum and minimum values in each cycle is the amplitude ofthe reference waveform or not. Therefore, even when the referencewaveform is changed, slice level data that are appropriate to the signalshape can be obtained on the basis of the detected amplitude in eachcycle and the average value thereof.

[0050] According to a 7th aspect of the present invention, in the dataslicer of the 5th or 6th aspect, when calculating the average value fromthe maximum and minimum values, the slice level calculation unit carriesout an averaging process for the calculated average and the slice leveldata that has been calculated in a previous cycle, and updates the slicelevel data on the basis of the obtained average. Therefore, even whenthe reference waveform is changed, slice level data that are appropriateto the signal shape can be obtained on the basis of the average value ineach cycle.

[0051] According to an 8th aspect of the present invention, in the dataslicer of the 5th aspect, the reference waveform and the data signalcorrespond to a signal of character broadcast which is transmitted beingsuperimposed upon a vertical blanking interval of a video signal.Therefore, the signal of character broadcast is binarized and then dataincluded in the signal are extracted therefrom, whereby the receivedsignal of character broadcast can be displayed.

[0052] According to a 9th aspect of the present invention, there isprovided a data slicer comprising: an A/D conversion unit for convertingan input signal of a predetermined cycle and amplitude, including datawhich are transmitted in serial, into a digital signal; a referencecycle detection unit for determining whether a cycle of the digitalsignal is the predetermined cycle or not; a maximum/minimum retrievalunit for retrieving maximum and minimum values of the digital signal; anamplitude evaluation unit for determining whether an amplitude of thedigital signal, which is calculated from the retrieved maximum andminimum values, is the predetermined amplitude or not; a slice leveldata calculation unit for calculating plural pieces of slice level dataon the basis of an average value and an amplitude of the digital signal,which are calculated from the maximum and minimum values at a time whenthe predetermined cycle and amplitude are detected; a binarization unitfor binarizing the digital signal using the plural pieces of slice leveldata, to be converted into plural binarized signals; an extraction pulsegeneration unit for generating an extraction pulse to be used forextracting the data from the binarized signals; an extraction unit forextracting the data from the plural binarized signals in accordance withthe extraction pulse, thereby generating plural pieces of serial data; adecoding unit for decoding the plural pieces of serial data, therebygenerating plural pieces of decoded data; a decoded data selection unitfor detecting an error from the plural pieces of decoded data, andselectively outputting one of the decoded data when errors are detectedfrom all of the decoded data, or decoded data including no error whenthere are decoded data in which no error is detected; an error countunit for counting errors in the data outputted from the decoded dataselection unit; and a controller for controlling the evaluation in theamplitude evaluation unit on the basis of the output from the errorcount unit. Therefore, when a desired signal is detected on the basis ofthe cycle and amplitude of the digital signal and thereby noises of apredetermine cycle are detected as the desired signal, slice level datacan be obtained only on the basis of the desired signal, with exceptingthe amplitude or average value obtained from the noises. Further, asplural pieces of slice level data are calculated, the data signal can bebinarized into a correct value using one of the plural pieces of slicelevel data, whereby even when distortion occurs in the data signal dueto group delay or reduction in electric field strength, the data can becorrectly extracted, thereby further suppressing the occurrence rate ofdecoding errors.

[0053] According to a 10th aspect of the present invention, in the dataslice of the 9th aspect, the input signal includes a reference waveformfor calculating the slice level data, this data slicer includes areference waveform detection unit for detecting the reference waveform,the reference cycle detection unit evaluates the cycle of the digitalsignal in a period when the reference waveform is detected, themaximum/minimum retrieval unit retrieves the maximum and minimum valuesof each cycle in the period when the reference waveform is detected, andthe amplitude evaluation unit determines whether the amplitudecalculated from the maximum and minimum values in each cycle is thepredetermined amplitude or not. Therefore, the slice level data can beobtained on the basis of the reference waveform.

[0054] According to an 11th aspect of the present invention, in the dataslicer of the 9th aspect, the input signal includes a reference waveformfor calculating the slice level data, a unit of the data is composed ofpredetermined bits, this data slicer includes: a reference waveformdetection unit for detecting the reference waveform; a data unitdetection unit for outputting a data unit detection pulse at intervalsof the data unit, on the basis of the decoded data, the maximum/minimumretrieval unit retrieves the maximum and minimum values in each cycle ina period when the reference waveform is detected, while retrieving themaximum and minimum values in each data unit on the basis of the dataunit detection pulse in a period when the decoded data are outputted,and the amplitude evaluation unit determines whether the amplitudecalculated from the maximum and minimum values in each cycle or eachdata unit is the predetermined amplitude or not. Therefore, slice leveldata are calculated using not only the reference waveform but also thedata signal, whereby even when the signal shape of the input signal ischanged after the calculation of the slice level data on the basis ofthe reference waveform, slice level data according to the signal shapecan be obtained and thus the occurrence rate of decoding errors can befurther suppressed.

[0055] According to a 12th aspect of the present invention, in the dataslicer of the 10th or 11th aspect, the slice level data calculation unitemploys the average value as reference slice level data, decides anoffset value on the basis of the amplitude calculated by the amplitudecalculation unit, and calculates upper slice level data by adding theoffset value to the reference slice level data and lower slice leveldata by subtracting the offset value from the reference slice leveldata. Therefore, slice level data according to the signal shape can beobtained.

[0056] According to a 13th aspect of the present invention, in the dataslicer of the 12th aspect, when calculating the average value from themaximum and minimum values, the slice level data calculation unitcarries out an averaging process for the calculated average value andthe reference slice level data that has been calculated in a previouscycle, and updates the reference slice level data on the basis of theobtained average value. Therefore, even when the reference waveform ischanged, slice level data that is appropriate to the signal shape can beobtained.

[0057] According to a 14th aspect of the present invention, in the dataslicer of the 12th or 13th aspect, when the predetermine cycle andamplitude are detected, the slice level data calculation unit carriesout an averaging process for the predetermined amplitude and anamplitude of the previous cycle, and decides the offset value on thebasis of the obtained average amplitude. Therefore, even when thereference waveform is changed, slice level data that is appropriate tothe signal shape can be obtained.

[0058] According to a 15th aspect of the present invention, in the dataslicer of the 9th aspect, the input signal is a signal of characterbroadcast that is transmitted being superimposed upon a verticalblanking interval of a video signal. Therefore, the signal of characterbroadcast is binarized and then data included in the signal areextracted, whereby the received character broadcast signal can bedisplayed.

[0059] According to a 16th aspect of the present invention, there isprovided a data slicing method for binarizing an input signal of apredetermined cycle using slice level data that are calculated on thebasis of the input signal, and extracting data included in the inputsignal, comprising: an A/D conversion step of converting the inputsignal that is transmitted in serial, into a digital signal; a referencecycle detection step of determining whether a cycle of the digitalsignal is the predetermined cycle or not; a maximum/minimum retrievalstep of retrieving maximum and minimum values of the digital signal; aslice level data calculation step of calculating plural pieces of slicelevel data on the basis of an average value and an amplitude of thedigital signal, which are calculated from the maximum and minimum valuesat a time when the predetermined cycle is detected; a binarization stepof converting the digital signal into plural binarized signals using theplural pieces of slice level data; a data extraction step of extractingdata in accordance with an extraction pulse for extracting data from thebinarized signals, thereby generating plural pieces of serial data; adecoding step of decoding the plural pieces of serial data, therebygenerating plural pieces of decoded data; and a decoded data selectionstep of determining the presence or absence of errors in the decodeddata, and selectively outputting decoded data including no error.Therefore, the data signal can be binarized into a correct value usingone of the plural pieces of slice level data, whereby the data arecorrectly extracted even when signal distortion occurs in the datasignal due to group delay or reduction in electric field strength,thereby suppressing the occurrence rate of decoding errors.

[0060] According to a 17th aspect of the present invention, there isprovide a data slicing method for binarizing an input signal of apredetermined cycle and amplitude using slice level data which arecalculated on the basis of the input signal, and extracting dataincluded in the input signal, comprising: an A/D conversion step ofconverting the input signal that is transmitted in serial, into adigital signal; a reference cycle detection step of determining whethera cycle of the digital signal is the predetermined cycle or not; amaximum/minimum retrieval step of retrieving maximum and minimum valuesof the digital signal; an amplitude evaluation step of determiningwhether an amplitude of the digital signal, which is calculated from theretrieved maximum and minimum values is the predetermined amplitude ornot; a slice level data calculation step of calculating plural pieces ofslice level data on the basis of an average value and an amplitude ofthe digital signal, which are calculated from the maximum and minimumvalues at a time when the predetermined cycle and amplitude aredetected; a binarization step of converting the digital signal intoplural binarized signals using the plural pieces of slice level data; adata extraction step of extracting data from the plural binarizedsignals in accordance with an extraction pulse for extracting data,thereby generating plural pieces of serial data; a decoding step ofdecoding the plural pieces of serial data, thereby generating pluralpieces of decoded data; a decoded data selection step of detectingerrors in the plural pieces of decoded data, and selectively outputtingone of the decoded data when errors are detected from all of the decodeddata, or decoded data including no error when there are decoded data inwhich no error is detected; and an amplitude evaluation control step ofcounting errors in the decoded data selected in the decoded dataselection step, and controlling the evaluation in the amplitudeevaluation step on the basis of the number of errors. Therefore, when adesired signal is detected on the basis of the amplitude of the digitalsignal and thereby noises of a predetermined cycle are detected as thedesired signal, the slice level data can be obtained on the basis ofonly the desired signal, with excepting the amplitude or average valueobtained from the noises. Further, as plural pieces of slice level dataare calculated, the data signal can be binarized into a correct valueusing one of the plural pieces of slice level data, whereby even whensignal distortion occurs in the data signal due to group delay orreduction in electric field strength, the data can be extractedcorrectly, and thus the occurrence rate of decoding errors can befurther suppressed.

[0061] According to a 18th aspect of the present invention, in the dataslicing method of the 16th or 17th aspect, in the slice level datacalculation step, the average value is employed as reference slice leveldata, an offset value is decided on the basis of the amplitude, thenupper slice level data is calculated by adding the offset value to thereference slice level data, and lower slice level data is calculated bysubtracting the offset value from the reference slice level data.Therefore, slice level data according to the signal shape can beobtained.

[0062] According to a 19th aspect of the present invention, there isprovided an amplitude evaluation value setting method comprising: astart value setting step of setting a start value at an amplitudeevaluation value for determining whether an input signal including datawhich are transmitted in serial is a desired signal or not; a signaldetection step of evaluating an amplitude of the input signal on thebasis of the amplitude evaluation value in a predetermined period,thereby detecting the desired signal; a slice level data calculationstep of, when detecting the desired signal, calculating slice level datafor binarizing the input signal, on the basis of the detected desiredsignal; a binarization step of binarizing the input signal using theslice level data, to be converted into a binarized signal; a decodingstep of decoding serial data which are extracted from the binarizedsignal, thereby generating decoded data; an error count step of countingerrors in the decoded data, and storing the amplitude evaluation valueand the number of errors; an amplitude evaluation value update step ofbinarizing and decoding the input signal and counting errors in thedecoded data during a predetermined period, thereafter subjecting theamplitude evaluation value to an arithmetic process using apredetermined step value, so as to approach an end value, and updatingthe amplitude evaluation value; and an amplitude evaluation valueselection step of selecting an amplitude evaluation value that minimizesthe number of errors as an optimum amplitude evaluation value, on thebasis of the numbers of errors at various amplitude evaluation values,which are obtained by changing the amplitude evaluation value in thepredetermined step value from the start value to the end value.Therefore, the amplitude evaluation value is changed to a value that isappropriate to the shape of the digital signal, whereby a desired signalcan be detected using the amplitude evaluation value that is appropriateto the signal shape, to calculate the slice level data, and accordinglythe occurrence of decoding errors can be suppressed even when thedistortion of the digital signal is changed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0063]FIG. 1 is a block diagram illustrating a construction of a dataslicer according to a first embodiment of the present invention.

[0064]FIG. 2 is a timing chart showing an operation of the data sliceraccording to the first embodiment in a case where an attenuated signalis inputted thereto.

[0065]FIG. 3 is a block diagram illustrating a construction of a dataslicer according to a second embodiment of the present invention.

[0066]FIG. 4 is a timing chart showing an operation of the data sliceraccording to the second embodiment in a case where an attenuated signalis inputted thereto.

[0067]FIG. 5 is a block diagram illustrating a construction of a dataslicer according to a third embodiment of the present invention.

[0068]FIG. 6 is a diagram showing the relationship between the CRIamplitude evaluation value and the number of errors, which are used forsetting a CRI amplitude evaluation value.

[0069]FIG. 7 is a timing chart showing an operation of the data sliceraccording to the third embodiment in a case where an attenuated signalis inputted thereto.

[0070]FIG. 8 is a flowchart for explaining a method by which a CRIamplitude evaluation value is set in the data slicer according to thethird embodiment.

[0071]FIG. 9 is a block diagram illustrating a construction of a dataslicer according to a fourth embodiment of the present invention.

[0072]FIG. 10 is a block diagram illustrating a construction of aconventional data slicer.

[0073]FIG. 11 is a timing chart showing an operation of the conventionaldata slicer in a case where a normal signal is inputted thereto.

[0074]FIG. 12 is a timing chart showing an operation of the conventionaldata slicer in a case where an attenuated signal is inputted thereto.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0075] Hereinafter, embodiments of the present invention will bedescribed with reference to the drawings. The embodiments shown here areonly exemplary, and the present invention is not restricted to theseembodiments.

[0076] [Embodiment 1]

[0077] A data slicer according to a first embodiment of the presentinvention will be described with reference to the drawings.

[0078]FIG. 1 is a block diagram illustrating a construction of the dataslicer according to the first embodiment.

[0079] As shown in FIG. 1, the data slicer 100 according to the firstembodiment includes an A/D converter 120 that converts an analog videosignal S110 inputted through a video signal input terminal 110, uponwhich character broadcast serial data are superimposed, into a digitalvideo signal S120; a CRI detection unit 130 that outputs a CRI detectionrange signal S132 indicating a clock run-in (hereinafter, referred to asCRI) detection period, on the basis of the digital video signal S120; alow-pass filter (hereinafter, referred to as LPF) 140 that eliminatesnoises from the digital video signal S120, and outputs a digital videosignal S140; a slice level calculation unit 150 that calculates a slicelevel and a slice level offset on the basis of the CRI signal C, andsets a reference slice level, and upper and lower slice levels which areobtained by providing the offset in the reference slice level; a dataslicing unit 160 that binarizes the digital video signal S140 using therespective slice levels that are set by the slice level calculation unit150; a decoding circuit 170 that converts respective binarized serialdata into parallel data, and carries out a decoding process such aserror correction depending on the type of character broadcast; and adata selection unit 180 that selects data including no error from therespective decoded data, and outputs the selected data through a videosignal output terminal 190.

[0080] The CRI detection unit 130 includes a sync separation circuit 131that separates a vertical sync signal S131 a and a horizontal syncsignal S131 b from the digital video signal S120; and a CRI detectionrange signal generation circuit 132 that outputs a CRI detection rangesignal S132 indicating a predetermined line and position as a detectionperiod of the CRI signal C, on the basis of the vertical sync signalS131 a and the horizontal sync signal S131 b.

[0081] The slice level calculation unit 150 includes a falling detectioncircuit 151 that outputs a falling detection pulse S151 when detecting afalling of the digital video signal S140 in the CRI detection period; afrequency calculation circuit 152 that calculates the frequency of thedigital video signal S140 from the falling detection pulse S151, andoutputs frequency data S152; a frequency evaluation circuit 153 thatcompares the frequency data S152 with previously-held frequency data ofa CRI signal C for the character broadcast system, and outputs afrequency evaluation gate pulse S153 during a period in which thefrequency data S152 that conforms to a predetermined character broadcastsystem are outputted; and a CRI evaluation circuit 154 that extracts apulse corresponding to a falling of a predetermined character broadcastsystem from the falling detection pulse S151, and outputs a frequencyevaluation pulse S154. The slice level calculation unit 150 furtherincludes a maximum/minimum retrieval circuit 155 that retrieves themaximum and minimum amplitudes of the digital video signal S140 in theCRI detection period, and outputs maximum value retrieval data S155 aand minimum value retrieval data S155 b; an average/amplitudecalculation circuit 156 that calculates an amplitude of the digitalvideo signal S140 and an average value of the amplitude from the maximumvalue retrieval data S155 a and the minimum value retrieval data S155 b,using the frequency evaluation pulse S154 as a load pulse, and outputsthe average value as reference slice level data S156 a and the amplitudeas amplitude detection data S156; and a slice level offset valuecalculation circuit 157 that calculates an offset value from theamplitude detection data S156 b, and calculates upper slice level dataS157 a and lower slice level data S157 b that are obtained by providingthe offset in the reference slice level data S156 a.

[0082] The data slicing unit 160 includes a binarization circuit 161that performs threshold evaluation using the upper slice level data S157a, the reference slice level data S156 a, and the lower slice level dataS157 b, respectively, to binarize the digital video signal S140, andoutputs binarized data S161 a to S161 c to an extraction circuit 163;and an extraction circuit 163 that extracts character broadcast serialdata from the respective binarized data S161 a to S161 c in timing of anextraction pulse S162 that is generated by an extraction pulsegeneration circuit 162, and outputs extracted serial data S163 a to S163c.

[0083] The data selection unit 180 includes an error detection circuit181 that determines whether decoded data S170 a to S170 c that areoutputted from the decoding circuit 170 include decoding errors or not,and outputs a decoded data selection signal S181 that indicates decodeddata including no decoding error; and a decoded data selection circuit182 that selects the decoded data including no decoding error from thedecoded data S170 a to S170 c, in accordance with the decoded dataselection signal S181, and outputs final decoded data S182 to outsidethe apparatus, through a video signal output terminal 190.

[0084] Next, the operation of the data slicer 100 that is constructed asdescribed above will be described with reference to the drawings.

[0085]FIG. 2 is a timing chart showing an operation of the data slicer100 in a case where an analog video signal S110 that is distorted due togroup delay or reduction in electric field strength is inputted thereto.In FIG. 2, the same or corresponding elements as those in FIG. 1 aredenoted by the same reference numerals. Reference character A denotes ahorizontal sync signal, B denotes a color burst signal, C denotes a CRIsignal, D denotes a framing code signal, E denotes a text data signal,and T1 to T8 denote times when the signals included in the digital videosignal S140 vary.

[0086] When an analog video signal S110 upon which character broadcastserial data are superimposed is inputted through the video signal inputterminal 110, the A/D converter 120 samples the analog video signal S110using a sampling clock fs (MHz) to convert the same into a digitalsignal. For example, an operation clock of the data slicer 100 is usedas the sampling clock fs. The digital video signal S120 that is obtainedby the A/D converter 120 is outputted to the CRI detection unit 130 andthe LPF 140. Then, the LPF 140 eliminates noises from the digital videosignal S120, and outputs a digital video signal S140 to the slice levelcalculation unit 150 and the data slicing unit 160. FIG. 2 shows anexample of the digital video signal S140 that is obtained byA/D-converting the distorted analog video signal S110, and eliminatingnoises from the converted signal. Reference character C′ denotes noisesthat occur during a period in which the CRI detection range signal S132is outputted, and cannot be eliminated by the LPF 140. The reason whythe digital video signal S140 is distorted even when the LPF 140performs the noise elimination is that the signal is affected by noisesthat cannot be eliminated even by the LPF 140. In this FIG. 2, blackdots show the digital video signal S120 (S140) that is obtained bysampling the analog video signal S110 using the sampling clock fs.

[0087] Since the digital video signal S120 including a horizontal syncsignal A and a vertical sync signal is inputted to the CRI detectionunit 130 at time T1, the sync separation circuit 131 separates avertical sync signal S131 a and a horizontal sync signal S131 b from thedigital video signal S120.

[0088] Next, the CRI detection range signal generation circuit 132obtains a start position and an end position of the CRI signal C on thebasis of the vertical sync signal S131 a and the horizontal sync signalS131 b, and outputs a CRI detection range signal S132 to the fallingdetection circuit 131 and the maximum/minimum retrieval circuit 133 in aCRI detection period. Here, the CRI detection range signal generationcircuit 132 may output the CRI detection range signal S132 continuouslyfrom a predetermined time (time T2) before the start of the CRI signal Cto a predetermined time after the end of the CRI signal C, as shown inFIG. 2.

[0089] During a predetermined period in the period while the CRIdetection range signal S132 is outputted, the digital video signal S140including the CRI signal C is inputted to the slice level calculationunit 150, and then the slice level calculation unit 150 performscalculation of a slice level on the basis of the inputted CRI signal C.In order to calculate the slice level, the falling detection circuit 151retrieves failings of the digital video signal S140, and themaximum/minimum retrieval circuit 155 retrieves the maximum and minimumvalues of the digital video signal S140, and outputs maximum valueretrieval data S155 a and minimum value retrieval data S155 b.

[0090] At time T3, the falling detection circuit 151 erroneously detectsa falling of the noises C′ in the digital video signal S140 as a fallingof the CRI signal C, and generates a falling detection pulse S151. Alsoat time T4, the falling detection circuit 151 erroneously detects afalling of the noises C′ as a falling of the CRI signal C, and generatesthe falling detection pulse S151.

[0091] Then, the frequency calculation circuit 152 calculates thefrequency of the digital video signal S140 on the basis of the fallingdetection pulses S151 that are detected at times T3 and T4, and outputsfrequency data S152. On the basis of the frequency data S152, thefrequency evaluation circuit 153 determines whether the failings thatare detected by the falling detection circuit 151 correspond to a signalthat is compliant with the predetermined character broadcast system ornot. When the interval between failings of the noises C′ is equal to theinterval between failings of the CRI signal C, like in the digital videosignal S140 shown in FIG. 2, the frequency evaluation circuit 153erroneously determines that the frequency of the noises C′ is afrequency that conforms to the predetermined character broadcast system,and outputs a frequency evaluation gate pulse S153 to the CRI evaluationcircuit 154.

[0092] Then, on the basis of the frequency evaluation gate pulse S153,the CRI evaluation circuit 154 determines whether the falling detectionpulse S151 is a pulse that is compliant with the character broadcastsystem or not. Since the interval between failings of the noises C′ isequal to the interval between failings of the CRI signal C in this case,the CRI evaluation circuit 154 erroneously determines that the fallingdetection pulse S151 is a pulse conforming to the character broadcast,and outputs a frequency evaluation pulse S154 to the average/amplitudecalculation circuit 156.

[0093] The average/amplitude calculation circuit 156 samples the maximumvalue retrieval data S155 a and the minimum value retrieval data S155 b,using the frequency evaluation pulse S154 as a load pulse, andcalculates the average value and the amplitude of the digital videosignal S140. Then, the average/amplitude calculation circuit 156 outputsthe calculated average value as reference slice level data S156 a to theslice level offset value calculation circuit 157 and the data slicingunit 160, and outputs the amplitudes as amplitude detection data S156 bto the slice level offset value calculation circuit 157.

[0094] When slight phase shift or level offset occurs in the vicinity ofa change point at which the digital video signal S140 changes from “0”to “1”, the binarization circuit 161 may binarize the signal into animproper value. To avoid this, the data slicer 100 according to thefirst embodiment binarizes the digital video signal 140, also usingslice level data which are obtained by providing an offset on the upperand lower sides of the reference slice level data S156 a, respectively.The offset is an amplitude having a predetermined ratio to the amplitudeof the CRI signal C. For example, the ratio is set at 20% of theamplitude. The slice level offset value calculation circuit 157 obtainsan offset value on the basis of the predetermined ratio and theamplitude detection data S156 b. Then, the slice level offset valuecalculation circuit 157 outputs upper slice level data S157 a that isobtained by adding the obtained offset value to the reference slicelevel data S156 a and lower slice level data S157 b that is obtained bysubtracting the offset value from the reference slice level data S156 a.As shown in FIG. 2, a slice level SLV2 that is set on the basis of thereference slice level data S156 a calculated using the noises C′, aslice level SLV1 that is set on the basis of the upper slice level dataS157 a, and a slice level SLV3 that is set on the basis of the lowerslice level data S157 b are lower level than an optimum slice level thatis set using the CRI signal C, and accordingly, these slice levelscannot be used for binarization of the digital video signal S140. Here,when the digital video signal S140 includes no distortion and no fallingof the noises C′ is detected at times T3 and T4, the above-mentionedprocessing at times T3 and T4 is not carried out, and the operationproceeds to processing at time T5, which will be now described.

[0095] At times T5 and T6, the CRI signal C is detected. The fallingdetection circuit 151 detects the first falling of the CRI signal C attime T5, then detects the second falling of the CRI signal C at time T6,and outputs falling detection pulses S151. While the maximum/minimumretrieval circuit 155 continuously performs the retrieval of the maximumand minimum values of the digital video signal S140 from time T2, butsince the minimum value of the noises C′ is smaller than the minimumvalue of the CRI signal in the digital video signal S140 as shown inFIG. 2, the minimum value retrieval data S155 b is not updated by theCRI signal C, but the minimum value of the noises C′ is continuouslyoutputted.

[0096] The frequency that is calculated by the frequency calculationcircuit 152 on the basis of the falling detection pulses S151 which aredetected at times T5 and T6 is a frequency that is compliant with thecharacter broadcast system. Therefore, the CRI evaluation circuit 154outputs a generated frequency evaluation pulse S154 to theaverage/amplitude calculation circuit 156. The average/amplitudecalculation circuit 156 samples the maximum value retrieval data S155 aand the minimum value retrieval data S155 b, using the frequencyevaluation pulse S154 as a load pulse, and calculates the average valueand the amplitude of the digital video signal S140. Then, theaverage/amplitude calculation circuit 156 outputs the calculated averagevalue to the slice level offset value calculation circuit 157 and thedata slicing unit 160 as reference slice level data S156 a, and outputsthe calculated amplitude to the slice level offset value calculationcircuit 157 as amplitude detection data S156 b. The slice level offsetvalue calculation circuit 157 calculates an offset value from theamplitude detection data S156 b, and outputs upper slice level data S157a that is obtained by adding the calculated offset value to thereference slice level data S156 a, and lower slice level data S157 bthat is obtained by subtracting the offset value from the referenceslice level data S156 a. Here, the minimum value retrieval data S155 bis the minimum value of the noises C′, and thus a slice level SLV5 thatis set on the basis of the calculated reference slice level data S156 ais lower than an optimum slice level. However, since the offsets areprovided, one of the slice level SLV4 that is set on the basis of theupper slice level data S157 a and the slice level SLV6 that is set onthe basis of the lower slice level data S157 b is an appropriate slicelevel that can be employed to binarize the framing code signal D and thetext data signal E after time T7.

[0097] When the digital video signal S140 including the framing codesignal D is inputted to the data slicing unit 160 at time T7, thebinarization circuit 161 determines whether the digital video signalS140 is higher or lower than the upper slice level data S157 a tobinarize the signal into “0” or “1”, thereby generating binarized dataS161 a. Similarly, the binarization circuit 161 binarizes the digitalvideo signal S140 on the basis of the reference slice level data S156 a,thereby generating binarized data S161 b, and binarizes the digitalvideo signal S140 on the basis of the lower slice level data S157 b,thereby generating binarized data S161 c. Further, the extraction pulsegeneration circuit 162 generates an extraction pulse S162 that isemployed as a sampling clock when character broadcast data are extractedfrom the respective binarized data S161 a to S161 c. Here, it is onlyrequired that the extraction pulse S162 have the same cycle as thetransmission clock for the character broadcast signal. Then, theextraction circuit 163 extracts character broadcast serial data from thebinarized data S161 a in accordance with the extraction pulse S162, andoutputs extracted serial data S163 a. Similarly, the extraction circuit163 extracts character broadcast serial data from the binarized dataS161 b in accordance with the extraction pulse S162, and outputsextracted serial data S163 b, while extracting character broadcastserial data from the binarized data S161 c in accordance with theextraction pulse S162 and outputting extracted serial data S163 c. Thedecoding circuit 170 converts the extracted serial data S163 a to S163 cinto parallel data, and detects the framing code.

[0098] When the digital video signal S140 including the text data signalE is inputted to the data slicing unit 160 at time T8, the binarizationcircuit 161 binarizes the digital video signal S140 like in the caseincluding the framing code signal D, using the upper slice level dataS157 a, the reference slice level data S156 a, and the lower slice leveldata S157 b, thereby generating binarized data S161 a to S161 c. Forexample, when a point P1 in the digital video signal S140 is binarizedusing the upper slice level data S157 a, “0” is obtained as thebinarized data S161 a. On the other hand, when this point P1 isbinarized using the reference slice level data S156 a and the lowerslice level data S156 b, “1” is obtained as the binarized data S161 band S161 c, respectively. In a case where data of the point P1 is “0”,correct data cannot be obtained when this data is binarized only usingthe reference slice level data S156 a. Even in such cases that the datais binarized into an improper value when the reference slice level dataS156 a is employed, a correct value can be also obtained by using theupper slice level data S157 a and the lower slice level data S157 b.Then, the extraction circuit 163 extracts character broadcast serialdata from the binarized data S161 a to S161 c in accordance with theextraction pulse S162, and outputs extracted serial data S163 a to S163b to the decoding circuit 170.

[0099] The decoding circuit 170 converts the extracted serial data S163a to S163 c into parallel data, then carries out a decoding processdepending on the type of character broadcast indicated by the framingcode, and outputs generated decoded data S170 a to S170 c to the dataselection unit 180.

[0100] When the decoded data S170 a to S170 c are inputted to the dataselection unit 180, the error detection circuit 181 detects the presenceor absence of errors in the respective decoded data S170 a to S170 c.More specifically, the error detection circuit 181 counts “1” in thedecoded data S170 a for each data unit, and determines that the decodeddata S170 a includes no decoding error when the number of “1” is an oddnumber of bits. Similarly, the error detection circuit 181 determineswhether the decoded data S170 b and S170 c include decoding errors ornot, on the basis of the number of “1” in each data unit. Then, theerror detection circuit 181 outputs a decoded data selection signal S181that designates decoded data including no decoding error. Here, theerror detection circuit 181 initially detects the presence or absence ofdecoding errors in the decoded data S170 b, and outputs the decoded dataselection signal S181 that designates the decoded data S170 b when thedata S170 b includes no decoding error. When the decoded data S170 binclude a decoding error, the error detection circuit 181 determineswhether the decoded data S170 a and S170 c includes a decoding error ornot, and designates data including no decoding error. When all of thedecoded data S170 a to S170 c include decoding errors, the errordetection circuit 181 designates one of these data. The decoded dataselection circuit 182 selects data including no decoding error from thedecoded data S170 a to S170 c in accordance with the decoded dataselection signal S181, and outputs final decoded data S182 to outsidethe data slicer 100 through the video signal output terminal 190.

[0101] The decoded data that is outputted from the video signal outputterminal 190 is transferred to a display circuit (not shown), anddisplayed as characters.

[0102] As described above, the data slicer 100 according to the firstembodiment includes the average/amplitude calculation circuit 156 thatcalculates the amplitude of the CRI signal C and the average value, andoutputs the average value as the reference slice level data S156 a andthe amplitude as the amplitude level data S156 b; the slice level offsetvalue calculation circuit 157 that calculates an offset value on thebasis of the amplitude level data S156 b, and calculates upper slicelevel data S157 a by adding the calculated offset value to the referenceslice level data S156 a, and lower slice level data S157 b bysubtracting the offset value from the reference slice level data S156 a;the binarization circuit 161 that binarizes the digital video signalS140 using reference slice level data S156 a, the upper slice level dataS157 a, and the lower slice level data S157 b; the decoding circuit 170that decodes extracted serial data S163 a to S163 c which are characterbroadcast serial data that are extracted from the binarized signal S161a to S161 c; and the decoded data selection circuit 182 that selectsdata including no decoding error from the respective decoded data S170 ato S170 c, and outputs the selected data. Therefore, even when thedigital video signal S140 is distorted due to group delay or reductionin electric field strength, and converted into an erroneous value whenthis video signal is binarized only with the reference slice level dataS156 a, this video signal can be binarized into a correct value usingone of the slice level data, and the decoded data based on the correctbinarized data is selectively outputted by the decoded data selectioncircuit 182, whereby the occurrence rate of decoding errors can besuppressed. Further, since the digital video signal can be binarizedinto a correct value using one of the plural slice level data, there isno need of a waveform equalization filter for correcting distortion ofthe waveform, thereby reducing the circuit scale of the data slicer.

[0103] [Embodiment 2]

[0104] A data slicer according to a second embodiment of the presentinvention will be described with reference to the drawings.

[0105]FIG. 3 is a block diagram illustrating a construction of a dataslicer 200 according to the second embodiment. In FIG. 3, the same orcorresponding elements as shown in FIG. 1 are denoted by the samereference numerals.

[0106] As shown in FIG. 3, the data slicer 200 according to the secondembodiment includes an A/D converter 120 that converts an analog videosignal S110 inputted through a video signal input terminal 110, uponwhich character broadcast serial data are superimposed, into a digitalvideo signal S120; a CRI detection unit 130 that generates a CRIdetection range signal S132 indicating a CRI detection period on thebasis of the digital video signal S120; a LPF 140 that eliminates noisesof a predetermined band from the digital video signal S120, and outputsa digital video signal S140; a slice level calculation unit 210 thatdetermines whether a detected signal is a CRI signal C or not, on thebasis of the amplitude of the digital video signal S140, and sets aslice level using the maximum and minimum values of only the CRI signalC; a data slicing unit 220 that binarizes the digital video signal S140using the slice level set by the slice level calculation unit 210; and adecoding circuit 230 that converts the binarized serial data intoparallel data to perform decoding, and outputs decoded data S230 througha video signal output terminal 190.

[0107] The slice level calculation unit 210 includes a falling detectioncircuit 151 that outputs a falling detection pulse S151 when detecting afalling of the digital video signal S140 during a CRI detection period;a frequency calculation circuit 152 that calculates the frequency of thedigital video signal S140 on the basis of the falling detection pulseS151, and outputs frequency data S152; a frequency evaluation circuit153 that outputs a frequency evaluation gate pulse S153 during a periodwhen a frequency conforming to a predetermined character broadcastsystem is obtained; and a CRI evaluation circuit 211 that outputs afrequency evaluation pulse S211 a which is obtained by extracting apulse corresponding to a falling of the predetermined characterbroadcast system from the falling detection pulse S151 in accordancewith the frequency evaluation gate pulse S153, and an amplitudeevaluation pulse S211 b that is obtained by extracting a falling pulseof the character broadcast signal (a falling pulse of the CRI signal C)from the falling detection pulse S151 in accordance with an amplitudeevaluation gate pulse S215 (which will be described later). The slicelevel calculation unit 210 further includes a maximum/minimum retrievalcircuit 212 that retrieves the maximum and minimum values of the digitalvideo signal S140 in the CRI detection period, and outputs maximum valueretrieval data S212 a and minimum value retrieval data S212 b; amaximum/minimum detection circuit 213 that detects the maximum andminimum values of the digital video signal S140 from the maximum valueretrieval data S212 a and the minimum value retrieval data S212 b, usingthe frequency evaluation pulse S211 a as a load pulse, and outputsmaximum value detection data S213 a and minimum value detection dataS213 b; an average/amplitude calculation circuit 214 that calculates theamplitude of the digital video signal S140 and the average value of theamplitude from the maximum value detection data S213 a and the minimumvalue detection data S213 b, using an amplitude evaluation gate pulseS215 that is outputted from an amplitude evaluation circuit 215 (whichwill be described later) as a load pulse, and outputs the average valueas slice level data S214 a and the amplitude as amplitude detection dataS214 b; and an amplitude evaluation circuit 215 that determines whetherthe amplitude detection data S214 b has an amplitude of thepredetermined character broadcast signal or not on the basis of a presetCRI amplitude evaluation value, and outputs an amplitude evaluation gatepulse S215 during a period in which the data has the amplitude of theCRI signal C.

[0108] Here, the CRI evaluation circuit 211 extracts a pulsecorresponding to a falling of the predetermined character broadcastsystem from the falling detection pulse S151, in accordance with thefrequency evaluation gate pulse S153, and outputs a frequency evaluationpulse S211 a to the maximum/minimum retrieval circuit 212 and themaximum/minimum detection circuit 213. This frequency evaluation pulseS211 a is delayed by a delay circuit (not shown) by a time period thatis required by the maximum/minimum detection circuit 213 to detect themaximum value retrieval data S212 a and the minimum value retrieval dataS212 b, and then inputted to the maximum/minimum retrieval circuit 212.When the amplitude evaluation gate pulse S215 is inputted, the CRIevaluation circuit 211 extracts a pulse corresponding to a signal havingan amplitude of the CRI signal C, from the frequency evaluation pulseS211 a, in accordance with the amplitude evaluation gate pulse S215, andoutputs the amplitude evaluation pulse S211 b.

[0109] The maximum/minimum retrieval circuit 212 retrieves the maximumand minimum values of the digital video signal S140, and outputs themaximum value retrieval data S212 a and the minimum value retrieval dataS212 b. Then, when the frequency evaluation pulse S211 a is inputted,the maximum/minimum retrieval circuit 212 once resets the maximum valueretrieval data S212 a and the minimum value retrieval data S212 b, thenretrieves the maximum and minimum values in a new period, and outputsmaximum value retrieval data S212 a and minimum value retrieval dataS212 b. In this way, the maximum/minimum retrieval circuit 212 retrievesthe maximum and minimum values in each period, on the basis of thefrequency evaluation pulse S211 a.

[0110] The average/amplitude calculation circuit 214 calculates theamplitude of the digital video signal S140 and the average value of theamplitude on the basis of the maximum value detection data S213 a andthe minimum value detection data S213 b, and outputs the amplitude tothe amplitude evaluation circuit 215 as amplitude detection data S214 b.Only when the amplitude detection pulse S211 b is inputted, theaverage/amplitude calculation circuit 214 outputs the calculated averagevalue to the binarization unit 220 as the slice level data S214 a.Further, when a new average value is calculated from new maximum valuedetection data S213 a and minimum value detection data S213 b inaccordance with the next frequency evaluation pulse S211 a, theaverage/amplitude calculation circuit 214 calculates the average betweenthe new average value and the slice level data S214 a, and updates theslice level data S214 a on the basis of the calculated value.

[0111] In the amplitude evaluation circuit 215, a CRI amplitudeevaluation value is previously set to be used as a judgement criterionat a time when it is judged whether the amplitude detection data S214 bhas the amplitude of the CRI signal C or not. The amplitude evaluationcircuit 215 determines whether the amplitude detection data S214 b hasthe amplitude of the CRI signal C or not, using the CRI amplitudeevaluation value, and outputs an amplitude evaluation gate pulse S215 tothe CRI evaluation circuit 211 during a period in which the data S214 bhas the amplitude of the CRI signal C.

[0112] The data slicing unit 220 includes a binarization circuit 221that performs threshold evaluation using the slice level data S214 a tobinarize the digital video signal S140, and outputs binarized data S221to an extraction circuit 222; and an extraction circuit 222 thatextracts character broadcast serial data from the binarized data S221 intiming of an extraction pulse S162 that is generated by an extractionpulse generation circuit 162, and outputs extracted serial data S222.

[0113] Hereinafter, the operation of the data slicer 200 that isconstructed as described above will be described with reference to thedrawings.

[0114]FIG. 4 is a timing chart showing an operation of the data slicer200 in a case where an analog video signal S110 that is distorted due togroup delay or reduction in electric field strength is inputted thereto.In FIG. 4, the same or corresponding elements as those in FIG. 3 aredenoted by the same reference numerals. Reference characters T11 to T19denote times when signals included in a digital video signal S140 vary.

[0115] When the analog video signal S110 upon which character broadcastserial data are superimposed is inputted through the video signal inputterminal 110, the A/D converter 120 converts this signal into a digitalsignal, and outputs the digital video signal S120 to the CRI detectionunit 130 and the LPF 140. Then, the LPF 140 outputs the digital videosignal S140 that is obtained by eliminating noises from the digitalvideo signal S120, to the slice level calculation unit 210 and the dataslicing unit 220.

[0116] At time T11, the digital video signal S120 including a horizontalsync signal A and a vertical sync signal is inputted to the CRIdetection unit 130, and then the sync separation circuit 131 separates avertical sync signal S131 a and a horizontal sync signal S13 lb from thedigital video signal S120.

[0117] Then, the CRI detection range signal generation circuit 132obtains a start position (time T12) and an end position of the CRIsignal C on the basis of the vertical sync signal S131 a and thehorizontal sync signal S131 b, and outputs a CRI detection range signalS132 during a CRI detection period.

[0118] While the CRI detection range signal S132 is inputted, the slicelevel calculation unit 210 performs slice level calculation on the basisof the CRI signal C, and accordingly the falling detection circuit 151retrieves a falling of the digital video signal S140. Themaximum/minimum retrieval circuit 212 retrieves the maximum and minimumvalues of the digital video signal S140, and outputs maximum valueretrieval data S212 a and minimum value retrieval data S212 b to themaximum/minimum detection circuit 213.

[0119] At times T13 and T14, the falling detection circuit 151erroneously detects a falling of noises C′ in the digital video signalS140 as a falling of the CRI signal C, and generates a falling detectionpulse S151. Then, the frequency calculation circuit 152 calculates thefrequency of the digital video signal S140 on the basis of the fallingdetection pulses S151 that are detected at times T13 and T14, andoutputs frequency data S152. On the basis of the frequency data S152,the frequency evaluation circuit 153 erroneously determines that thefailings detected by the falling detection circuit 151 correspond to asignal of a predetermined character broadcast system, and outputs afrequency evaluation gate pulse S153 to the CRI evaluation circuit 211.On the basis of the frequency evaluation pulse S153, the CRI evaluationcircuit 211 erroneously determines the falling detection pulse S151 is apulse conforming to the character broadcast system, and outputs afrequency evaluation pulse S211 a to the maximum/minimum retrievalcircuit 211 and the maximum/minimum detection circuit 213.

[0120] The maximum/minimum detection circuit 213 samples the maximumvalue retrieval data S212 a and the minimum value retrieval data S212 bwhich are retrieved in a period from time T13 to time T14, using thefrequency evaluation pulse S221 a as a load pulse, thereby to detect themaximum and minimum values of the digital video signal S140, and outputsmaximum value detection data S213 a and minimum value detection dataS213 b. Further, when the frequency evaluation pulse S211 a is inputtedto the maximum/minimum retrieval circuit 212 after the maximum/minimumdetection circuit 213 samples the maximum value retrieval data S212 aand the minimum value retrieval data S212 b, the maximum/minimumretrieval circuit 212 resets the maximum and minimum values retrieved inthe period from T13 to T14, and retrieves maximum and minimum values ofthe digital video signal S140 after time T14. The average/amplitudecalculation circuit 214 calculates the amplitude of the digital videosignal S140 from the maximum value detection data S213 a and the minimumvalue detection data S213 b, and outputs the calculated value to theamplitude evaluation circuit 215 as amplitude detection data S214 b.Since an amplitude detection pulse S211 b is not yet generated at thispoint of time, slice level data S214 a is not outputted.

[0121] Next, the amplitude evaluation circuit 215 determines whether theamplitude detection data S214 b has the amplitude of the CRI signal C ornot, using a preset CRI amplitude evaluation value. In this case, sincethe amplitude detection data S214 b is detected on the basis of thenoises C′ and has a smaller value than the amplitude detection data thatis detected on the basis of the CRI signal C, the amplitude detectiondata S214 b does not meet requirements of the CRI amplitude evaluationvalue. Accordingly, the amplitude evaluation circuit 215 determines thatthe amplitude detection data S214 b does not have the amplitude of theCRI signal, and does not generate the amplitude evaluation gate pulseS215.

[0122] At times T15 and T16, the CRI signal C is detected. The fallingdetection circuit 151 detects the first falling of the CRI signal C attime T15, then detects the second falling of the CRI signal C at timeT16, and outputs falling detection pulses S151. Since the frequency thatis calculated by the frequency calculation circuit 152 on the basis ofthe falling detection pulses S151 is a frequency that conforms to thecharacter broadcast system, the frequency evaluation pulse S211 a isinputted to the maximum/minimum retrieval circuit 212 and themaximum/minimum detection circuit 213.

[0123] The maximum/minimum detection circuit 213 samples the maximumvalue retrieval data S212 a and the minimum value retrieval data S212 bwhich are retrieved in a period from time T15 to time T16, using thefrequency evaluation pulse S211 a as a load pulse, thereby to detect themaximum and minimum values of the digital video signal S140, and outputsmaximum value detection data S213 a and minimum value detection dataS213 b. The maximum/minimum retrieval circuit 212 resets the maximumvalue retrieval data S212 a and the minimum value retrieval data S212 bwhich are retrieved in the period from time T15 to time T16, on thebasis of the frequency evaluation pulse S211 a, and retrieves maximumand minimum values of the digital video signal S140 after the time T16.The average/amplitude calculation circuit 214 calculates the amplitudeof the digital video signal on the basis of the maximum value detectiondata S213 a and the minimum value detection data S213 b, and outputs thecalculated value to the amplitude evaluation circuit 215 as amplitudedetection data S214 b.

[0124] Since this amplitude detection data S214 b has the amplitude ofthe CRI signal C, the amplitude evaluation circuit 215 outputs theamplitude evaluation gate pulse S215 to the CRI evaluation circuit 211.Then, the CRI evaluation circuit 211 outputs an amplitude evaluationpulse S21 lb that is obtained by extracting a pulse of the CRI signal Cfrom the frequency evaluation pulse S211 a, in accordance with theamplitude evaluation gate pulse S215. When the amplitude evaluationpulse S211 b is inputted, the average/amplitude calculation circuit 214outputs the average value of the calculated amplitudes of the digitalvideo signal S140 to the data slicing unit 220 as slice level data S214a. Here, the slice level data S214 a is calculated not using the maximumvalue retrieval data and the minimum value retrieval data which aredetected on the basis of the noises C′ of the CRI signal, but using themaximum value retrieval data S212 a and the minimum value retrieval dataS212 b of the CRI signal C. Accordingly, a slice level SLV7 that is seton the basis of the slice level data S214 a is an appropriate level thatcan be employed to binarize the framing code signal D and the text datasignal E after time T17.

[0125] At time T17, the falling detection circuit 151 detects the thirdfalling of the CRI signal C, and outputs the falling detection pulseS151. As the frequency that is calculated by the frequency calculationcircuit 152 on the basis of the falling detection pulses S151 that areoutputted at times T16 and T17 is a frequency conforming to thecharacter broadcast system, the frequency evaluation pulse S211 a isinputted to the maximum/minimum retrieval circuit 212 and themaximum/minimum detection circuit 213.

[0126] The maximum/minimum detection circuit 213 outputs maximum valuedetection data S213 a and minimum value detection data S213 b using thefrequency evaluation pulse S211 a as a load pulse, to theaverage/amplitude calculation circuit 214. Then, the maximum/minimumretrieval circuit 212 resets the maximum value retrieval data S212 a andthe minimum value retrieval data S212 b on the basis of the frequencyevaluation pulse S211 a, and retrieves maximum and minimum values aftertime T17. The average/amplitude calculation circuit 214 calculates theamplitude of the digital video signal S140 on the basis of the maximumvalue detection data S213 a and the minimum value detection data S213 b,and outputs the calculated value to the amplitude evaluation circuit 215as amplitude detection data S214 b.

[0127] Since the amplitude detection data S214 has the amplitude of theCRI signal C, the amplitude evaluation circuit 215 outputs the amplitudeevaluation gate pulse S215 to the CRI evaluation circuit 211, and theCRI evaluation circuit 211 outputs the amplitude evaluation pulse S211 bin accordance with the amplitude evaluation gate pulse S215.

[0128] When the amplitude evaluation pulse S211 b is inputted, theaverage/amplitude calculation circuit 214 calculates the average valueof the amplitudes of the digital video signal S140. Theaverage/amplitude calculation circuit 214 further calculates the averagebetween the average value calculated at time T17 and the slice leveldata calculated at time T16, and updates the slice level data S214 a onthe basis of the calculated value. Here, FIG. 4 shows a case where themaximum and minimum values of the digital video signal S140 in theperiod from time T16 to T17 are smaller than the maximum and minimumvalues in the period from time T15 to time T16, and a slice level SLV8that is set on the basis of the slice level data S214 a calculated attime T17 is lower than the slice level SLV7.

[0129] At time T18, the falling detection circuit 151 detects the fourthfalling of the CRI signal C, and outputs the falling detection pulseS151. The slice level calculation unit 210 carries out the sameprocessing as performed at time T17, on the basis of the fallingdetection pulse S151, and the maximum value detection data S212 a andthe minimum value detection data S212 b which are retrieved by themaximum/minimum retrieval circuit 212, and updates the slice level dataS214 a.

[0130] When the CRI detection range signal S132 ends at time T19, theslice level calculation unit 210 finishes the slice level calculationprocess. Accordingly, the slice level data S214 a at time T19 becomesfixed data which will not be changed after time T19. Here, when themaximum and minimum values of the digital video signal S140 in theperiod from time T17 to time T18 is lower than the maximum and minimumvalues in the period from time T16 to time T17 as shown in FIG. 4, aslice level SLV9 that is set on the basis of the slice level data S214 acalculated at time T18 is lower than the slice level SLV8.

[0131] When the digital video signal S140 including a framing codesignal D is inputted to the data slicing unit 220 at time T19, thebinarization circuit 211 determines whether the digital video signalS140 is higher or lower than the slice level data S214 a, therebygenerating binarized data S221. Then, the extraction circuit 222extracts character broadcast serial data from the binarized data S221 inaccordance with an extraction pulse S162 that is generated by theextraction pulse generation circuit 162, and outputs the extractedserial data S222 to the decoding circuit 230. The decoding circuit 230converts the extracted serial data S222 into parallel data, and detectsthe framing code.

[0132] When the digital video signal S140 including a text data signal E(not shown) is inputted to the data slicing unit 220 after the detectionof the framing code, the binarization circuit 221 binarizes the digitalvideo signal S140 using the slice level data S214 a like in the caseincluding the framing code signal D, to generate binarized data S221.Then, the extraction circuit 222 extracts character broadcast serialdata from the binarized data S221 in accordance with an extraction pulseS162, and outputs extracted serial data S222 to the decoding circuit230. The decoding circuit 230 converts the extracted serial data S222into parallel data, then performs a decoding process according to thetype of the character broadcast indicated by the framing code, andoutputs decoded data S230 to outside the data slicer 200 through thevideo signal output terminal 190.

[0133] As described above, the data slicer 200 according to the secondembodiment includes the amplitude evaluation circuit 215 that determineswhether the amplitude detection data S214 b calculated by theaverage/amplitude calculation circuit 214 has the amplitude of the CRIsignal C or not, and thus the average/amplitude calculation circuit 214outputs the calculated average value as slice level data S214 a onlywhen it is determined that the amplitude detection data S214 b has theamplitude of the CRI signal C. Therefore, even when noises that occurdue to signal distortion resulting from group delay or reduction inelectric field strength in the transmission system are erroneouslydetected as the CRI signal C, it is possible to eliminate the averagevalue that is calculated on the basis of the noises, and calculate slicelevel data S214 a on the basis of the average value of only the CRIsignal C.

[0134] Further, even when the noises are erroneously detected as the CRIsignal, slice level data is not calculated on the basis of the detectednoises. Therefore, also in the case of a character broadcast signal inwhich the CRI signal is not superimposed over a line in a verticalblanking interval that is defined in the standard, like in a teletextsystem adopted in Europe, the calculation of slice level data on thebasis of noises can be suppressed.

[0135] [Embodiment 3]

[0136] A data slicer and an amplitude evaluation value setting methodaccording to a third embodiment of the present invention will bedescribed with reference to the drawings.

[0137]FIG. 5 is a block diagram illustrating a construction of a dataslicer 300 according to the third embodiment. In FIG. 5, the same orcorresponding elements as those in FIG. 3 are denoted by the samereference numerals.

[0138] As shown in FIG. 5, the data slicer 300 according to the thirdembodiment includes an A/D converter 120 that converts an analog videosignal S110 inputted through a video signal input terminal 110, uponwhich character broadcast serial data are superimposed, into a digitalvideo signal S120; a CRI detection unit 130 that generates a CRIdetection range signal S132 indicating a CRI detection period, on thebasis of the digital video signal S120; a LPF 140 that eliminates noisesfrom the digital video signal S120, and outputs a digital video signalS140; a slice level calculation unit 310 that determines whether thedetected signal is a CRI signal C or not, on the basis of the amplitudeof the digital video signal S140, calculates a slice level and an offsetof the slice level using the maximum and minimum values of only the CRIsignal C, and sets a reference slice level, and upper and lower slicelevels which are obtained by providing the offset in the reference slicelevel; a data slicing unit 160 that binarizes the digital video signalS140 using the respective slice levels which are set by the slice levelcalculation unit 310; a decoding unit 170 that converts the respectivebinarized serial data into parallel data, and performs a decodingprocess such as error correction according to the type of the characterbroadcast; a data selection unit 320 that selects data including noerror from respective decoded data, and outputs the selected datathrough a video signal output terminal 190; and an amplitude evaluationvalue setting unit 330 that sets an amplitude evaluation value that isemployed when the slice level calculation unit 310 determines theamplitude of the digital video signal S140, on the basis of the numberof errors detected by the decoding circuit 170, and outputs an optimumamplitude evaluation value S332.

[0139] The slice level calculation unit 310 includes a falling detectioncircuit 151 that outputs a falling detection pulse S151 when detecting afalling of the digital video signal S140 during a CRI detection period;a frequency calculation circuit 152 that calculates the frequency of thedigital video signal S140 on the basis of the falling detection pulseS151, and outputs frequency data S152; a frequency evaluation circuit153 that outputs a frequency evaluation gate pulse S153 during a periodin which a frequency that is compliant with a predetermined characterbroadcast system is obtained; and a CRI evaluation circuit 211 thatoutputs a frequency evaluation pulse S211 a that is obtained byextracting a pulse corresponding to a falling of a predeterminedcharacter broadcast, from the falling detection pulse S151, and anamplitude evaluation pulse S211 b that is obtained by extracting a pulseof character broadcast (CRI signal C) in accordance with an amplitudeevaluation gate pulse S312 (which will be later described). The slicelevel calculation unit 310 further includes a maximum/minimum retrievalcircuit 212 that retrieves the maximum and minimum values of the digitalvideo signal S140 in the CRI detection period, and outputs maximum valueretrieval data S212 a and minimum value retrieval data S212 b; amaximum/minimum detection circuit 213 that detects the maximum andminimum values of the digital video signal S140 from the maximum valueretrieval data S212 a and the minimum value retrieval data S212 b, usingthe frequency evaluation pulse S211 a as a load pulse, and outputsmaximum value detection data S213 a and minimum value detection dataS213 b; an average/amplitude calculation circuit 311 that calculates theamplitude of the digital video signal S140 and the average amplitudefrom the maximum value detection data S21 a and the minimum valuedetection data S213 b, and outputs the average value as reference slicelevel data S311 a, the amplitude as amplitude detection data S311 b, andthe amplitude of the CRI signal C as amplitude level data S311 c; aslice level offset value calculation circuit 157 that calculates anoffset value from the amplitude level data S311 c, and calculates upperslice level data S157 a and lower slice level data S157 b that areobtained by providing the offset in the reference slice level data S311a; and an amplitude evaluation circuit 312 that determines whether theamplitude detection data S311 b has the amplitude of a signal of apredetermined character broadcast or not, on the basis a preset CRIamplitude evaluation value or an optimum amplitude evaluation value S332that is inputted from the amplitude evaluation setting unit 330, andoutputs an amplitude evaluation gate pulse S312 during a period in whichthe data S311 b has the amplitude of the CRI signal C.

[0140] Here, the average/amplitude calculation unit 311 calculates theamplitude of the digital video signal S140 and the average amplitude onthe basis of the maximum value detection data S213 a and the minimumvalue detection data S213 b, and outputs the amplitude to the amplitudeevaluation circuit 312 as amplitude detection data S311 b. Only when theamplitude evaluation pulse S211 b is inputted, the average/amplitudecalculation unit 311 outputs the calculated average to the slice leveloffset value calculation circuit 157 and the binarization unit 220 asreference slice level data S311 a. Further, the average/amplitudecalculation unit 311 outputs the calculated amplitude to the slice leveloffset value calculation circuit 157 as amplitude level data S311 c whenthe amplitude evaluation pulse S211 b is inputted thereto.

[0141] When the average/amplitude calculation circuit 311 calculates anew amplitude and a new average value on the basis of new maximum valuedetection data S213 a and minimum value detection data S213, inaccordance with the next frequency evaluation pulse S211 a, thecalculation circuit 311 further calculates the average between the newaverage value and the reference slice level data S311 a, and updates thereference slice level data S311 a on the basis of the calculated value.Similarly, the calculation circuit 311 calculates the average betweenthe new amplitude and the amplitude level data S311 c, and updates theamplitude level data S311 c on the basis of the calculated value.

[0142] In the amplitude evaluation circuit 312, a CRI amplitudeevaluation value is previously set to be used as a judgement criterionwhen it is judged whether the amplitude detection data S311 b has theamplitude of the CRI signal C or not. The amplitude evaluation circuit312 determines whether the amplitude detection data S311 b has theamplitude of the CRI signal C or not, using the CRI amplitude evaluationvalue, and outputs an amplitude evaluation gate pulse S312 to the CRIevaluation circuit 211 during a period in which the data S311 b has theamplitude of the CRI signal C. When the optimum amplitude evaluationvalue S332 is inputted from the amplitude evaluation value setting unit330, the amplitude evaluation circuit 312 updates the CRI amplitudeevaluation value on the basis of the optimum amplitude evaluation valueS332, and evaluates the amplitude of the amplitude detection data S311 busing the updated CRI amplitude evaluation value.

[0143] The data selection unit 320 includes an error detection circuit321 that outputs an error detection signal S321 b indicating whetherfinal decoded data S182 includes a decoding error or not, as well as adecoded data selection signal S321 a that indicates decoded dataincluding no decoding error; and a decoded data selection circuit 182that selects decoded data including no error from decoded data S170 a toS170 c in accordance with the decoded data selection signal S321 a, andoutputs the final decoded data S182 to outside the data slicer throughthe video signal output terminal 190.

[0144] The amplitude evaluation value setting unit 330 includes an errorcount circuit 331 that counts decoding errors which are detected in apredetermined period on the basis of the error detection signal S321 b,and generates error count data S331; and a controller 332 that decidesan optimum value for the CRI amplitude evaluation value on the basis ofthe error count data S331, and outputs an optimum amplitude evaluationvalue S332 to the amplitude evaluation circuit 312 in the slice levelcalculation unit 310.

[0145] Here, the controller 332 holds the relationship between the CRIamplitude evaluation value and the error count data in a case where theCRI amplitude evaluation value takes various values. FIG. 6 shows anexample of the relationship between the CRI amplitude evaluation valueand the error count data. A method for obtaining the relationshipbetween the CRI amplitude evaluation value and the error count data willbe described later. When the error count data S331 is inputted, thecontroller 332 detects an optimum CRI amplitude evaluation value in acase where the number of errors is equal to the error count data S331 onthe basis of the relationship between the CRI amplitude evaluation valueand the error count data. Then, the controller 332 outputs the detectedoptimum CRI amplitude evaluation value to the amplitude evaluationcircuit 312 as the optimum amplitude evaluation value S332.

[0146] Next, an operation of the data slicer 300 that is constructed asdescribed above will be explained with reference to the drawings.

[0147]FIG. 7 is a timing chart showing an operation of the data slicer300 in a case where an analog video signal S110 that is distorted due togroup delay or reduction in electric field strength is inputted thereto.In FIG. 7, the same or corresponding elements as those shown in FIG. 5are denoted by the same reference numerals. Further, referencecharacters T21 to T29 denote times when signals included in the digitalvideo signal S140 vary.

[0148] When the analog video signal S110 upon which character broadcastserial data are superimposed is inputted through the video signal inputterminal 110, the A/D converter 120 converts the analog video signalS110 into a digital signal, and outputs the digital video signal S120 tothe CRI detection unit 130 and the LPF 140. Then, the LPF 140 eliminatesnoises from the digital video signal S120, and outputs a resultantdigital video signal S140 to the slice level calculation unit 310 andthe data slicing unit 160.

[0149] As the digital video signal S120 including a horizontal syncsignal A and a vertical sync signal is inputted to the CRI detectionunit 130 at time T21, the sync separation circuit S131 separates avertical sync signal S131 a and a horizontal sync signal S131 b from thedigital video signal S120.

[0150] Then, the CRI detection range signal generation circuit 132obtains a start position (time T22) and an end position of the CRIsignal C on the basis of the vertical sync signal S131 a and thehorizontal sync signal S131 b, and outputs a CRI detection range signalS132 in the CRI detection period.

[0151] As the slice level calculation unit 310 performs a slice levelcalculation process on the basis of the CRI signal C while the CRIdetection range signal S132 is inputted, the falling detection circuit151 retrieves a falling of the digital video signal S140. Themaximum/minimum retrieval circuit 212 retrieves the maximum and minimumvalues of the digital video signal S140, and outputs maximum valueretrieval data S212 a and minimum value retrieval data S212 b to themaximum/minimum detection circuit 213.

[0152] At times T23 and T24, the falling detection circuit 151erroneously detects a falling of noises C′ in the digital video signalS140 as a falling of the CRI signal C, and generates a falling detectionpulse S151. Then, the frequency calculation circuit 152 calculates thefrequency of the digital video signal S140 on the basis of the fallingdetection pulses S151 that are detected at times T23 and T24, andoutputs frequency data S152. On the basis of the frequency data S152,the frequency evaluation circuit 153 determines that the failingsdetected by the falling detection circuit 151 correspond to a signalthat is compliant with a predetermined character broadcast system, andoutputs a frequency evaluation gate pulse S153 to the CRI evaluationcircuit 211. On the basis of the frequency evaluation gate pulse S153,the CRI evaluation circuit 211 determines that the falling detectionpulse S151 is a pulse that is compliant with the character broadcastsystem, and outputs a frequency evaluation pulse S211 a to themaximum/minimum retrieval circuit 212 and the maximum/minimum detectioncircuit 213.

[0153] The maximum/minimum detection circuit 213 samples the maximumvalue retrieval data S212 a and the minimum value retrieval data S212 bwhich are retrieved in a period from time T23 to time T24, using thefrequency evaluation pulse S211 a as a load pulse, thereby to detect themaximum and minimum values of the digital video signal S140, and outputsmaximum value detection data S213 a and minimum value detection dataS213 b. Further, the maximum/minimum retrieval circuit 212 resets themaximum value retrieval data S212 a and the minimum value retrieval dataS212 b which are retrieved in the period from time T23 to time T24, onthe basis of the frequency evaluation pulse S211 a, and retrievesmaximum and minimum values of the digital video signal S140 after timeT24. The average/amplitude calculation circuit 311 calculates theamplitude of the digital video signal S140 on the basis of the maximumvalue detection data S213 a and the minimum value detection data S213 b,and outputs the calculated value to the amplitude evaluation circuit 312as amplitude detection data S311 b. Since an amplitude detection pulseS211 b is not yet generated at this point of time, reference slice leveldata S311 a or amplitude level data S311 c are not outputted.

[0154] Then, the amplitude evaluation circuit 312 determines whether theamplitude detection data S311 b has the amplitude of the CRI signal C ornot, using a preset CRI amplitude evaluation value. In this case, as theamplitude detection data S31 lb is detected from the noises C′ andaccordingly has a smaller value than the amplitude detection data thatis detected from the CRI signal C, the amplitude detection data S311 bdoes not meet requirements of the CRI amplitude evaluation value. Thus,the amplitude evaluation circuit 312 determines that this amplitudedetection data S311 b does not have the amplitude of the CRI signal C,and does not generate the amplitude evaluation gate pulse S312.

[0155] At times T25 and T26, the CRI signal C is detected. The fallingdetection circuit 151 detects the first falling of the CRI signal C attime T25, then detects the second falling of the CRI signal C at timeT26, and outputs the falling detection pulses S151. The frequencycalculated by the frequency calculation circuit 152 on the basis of thefalling detection pulses S151 is a frequency that conforms to thecharacter broadcast system, so that a frequency evaluation pulse S211 ais inputted to the maximum/minimum retrieval circuit 212 and themaximum/minimum detection circuit 213.

[0156] The maximum/minimum detection circuit 213 samples the maximumvalue retrieval data S212 a and the minimum value retrieval data S212 bwhich are retrieved in the period from time T25 to time T26, using thefrequency evaluation pulse S211 a as a load pulse, thereby to detect themaximum and minimum values of the digital video signal S140, and outputsmaximum value detection data S213 a and minimum value detection dataS213 b. Further, the maximum/minimum retrieval circuit 212 resets themaximum value retrieval data S212 a and the minimum value retrieval dataS212 b which are retrieved in the period from time T25 to time T26, onthe basis of the frequency evaluation pulse S211 a, and retrievesmaximum and minimum values of the digital video signal S140 after timeT26. The average/amplitude calculation circuit 311 calculates theamplitude of the digital video signal from the maximum value detectiondata S213 a and the minimum value detection data S213 b, and outputs thecalculated amplitude to the amplitude evaluation circuit 312 asamplitude detection data S311 b.

[0157] The amplitude evaluation circuit 312 determines that theamplitude detection data S311 b has the amplitude of the CRI signal C,and outputs an amplitude evaluation gate pulse S312 to the CRIevaluation circuit 211. Then, the CRI evaluation circuit 211 outputsamplitude evaluation pulses S21 lb that are obtained by extractingpulses of the CRI signal C from the frequency evaluation pulse S211 a inaccordance with the amplitude evaluation gate pulse S312, to theaverage/amplitude calculation circuit 311.

[0158] When the amplitude evaluation pulse S211 b is inputted, theaverage/amplitude calculation circuit 311 outputs the average value ofthe calculated amplitudes of the digital video signal S140 to the slicelevel offset value calculation circuit 157 and the data slicing unit160, as reference slice level data S311 a, while outputting theamplitude to the slice level offset value calculation circuit 157 asamplitude level data S311 c. The slice level offset value calculationcircuit 157 calculates an offset value from the amplitude level dataS311 c, and outputs upper slice level data S157 a that is obtained byadding the offset value to the reference slice level data S311 a andlower slice level data S157 b that is obtained by subtracting the offsetvalue from the reference slice level data S311 a.

[0159] At time T27, the falling detection circuit 151 detects the thirdfalling of the CRI signal C, and outputs the falling detection pulseS151. As the frequency that is calculated by the frequency calculationcircuit 152 on the basis of the falling detection pulses S151 that areoutputted at times T26 and T27 is a frequency corresponding to thecharacter broadcast system, the frequency evaluation pulse S211 a isinputted to the maximum/minimum retrieval circuit 212 and themaximum/minimum detection circuit 213.

[0160] The maximum/minimum detection circuit 213 detects maximum valuedetection data S213 a and minimum value detection value S213 b using thefrequency evaluation pulse S211 a as a load pulse, and outputs thedetected data S213 a and S213 b to the average/amplitude calculationcircuit 311. The maximum/minimum retrieval circuit 212 resets themaximum value retrieval data S212 a and the minimum value retrieval dataS212 b on the basis of the frequency evaluation pulse S211 a, andretrieves maximum and minimum values after time T27. Theaverage/amplitude calculation circuit 311 calculates the amplitude ofthe digital video signal S140 from the maximum value detection data S213a and the minimum value detection data S213 b, and outputs thecalculated amplitude to the amplitude evaluation circuit 312 asamplitude detection data S311 b.

[0161] As the amplitude detection data S311 b has the amplitude of theCRI signal C, the amplitude evaluation circuit 312 outputs an amplitudeevaluation gate pulse S312 to the CRI evaluation circuit 211, and theCRI evaluation circuit 211 outputs the amplitude evaluation pulse S211 bin accordance with the amplitude evaluation gate pulse S312.

[0162] When the amplitude evaluation pulse S211 b is inputted, theaverage/amplitude calculation circuit 311 calculates the averageamplitude of the digital video signal S140. The average/amplitudecalculation circuit 311 further calculates the average value between theaverage value calculated at time T27 and the reference slice level datacalculated at time T26, and updates the reference slice level data S311a on the basis of the calculated value. The average/amplitudecalculation circuit 311 further calculates the average value between theamplitude of the digital video signal S140 at time T27 and the amplitudelevel data S311 c calculated at time T26, and updates the amplitudelevel data S311 c on the basis of the calculated value. Then, the slicelevel offset value calculation circuit 157 calculates upper slice leveldata S157 a and lower slice level data S157 b on the basis of an offsetvalue that is calculated from the amplitude level data S311 c.

[0163] At time T28, the falling detection circuit 151 detects the fourthfalling of the CRI signal C, and outputs the falling detection pulseS151. On the basis of the falling detection pulse, and the maximum valuedetection data S212 a and the minimum value detection data S212 b whichare retrieved by the maximum/minimum retrieval circuit 212, the slicelevel calculation unit 310 carries out the same processing as thatperformed at time T27 and outputs reference slice level data S311 a,upper slice level data S157 a, and lower slice level data S157 b.

[0164] When the CRI detection range signal S132 ends at time T29, theslice level calculation unit 310 finishes the slice level calculationprocess. Thus, the reference slice level data S311 a, the upper slicelevel data S157 a, and the lower slice level data S157 b at time T29become fixed data which will never be changed after that time.

[0165] When the digital video signal S140 including the framing codesignal D is inputted to the data slicing unit 160 at time T29, thebinarization circuit 161 binarizes the digital video signal S140 usingthe upper slice level data S157 a, the reference slice level data S311a, and the lower slice level data S157 b, to generate binarized dataS161 a to S161 c, respectively. Then, the extraction circuit 163extracts character broadcast serial data from the binarized data S161 ato S161 c, in accordance with an extraction pulse S162 that is generatedby the extraction pulse generation circuit 162, and outputs extractedserial data S163 a to S163 c to the decoding circuit 170. The decodingcircuit 170 converts the extracted serial data S163 a to S163 c intoparallel data, and detects the framing code.

[0166] When the digital video signal S140 including a text data signal Eis inputted to the data slicing unit 160, the binarization circuit 161binarizes the digital video signal S140 using the upper slice level dataS157 a, the reference slice level data S311 a, and the lower slice leveldata S157 b, like in the case including the framing code signal D,thereby to generate binarized data S161 a to S161 c, respectively. Then,the extraction circuit 163 extracts character broadcast serial data fromthe binarized data S161 a to S161 c in accordance with the extractionpulse S162, and outputs extracted serial data S163 a to S163 c to thedecoding circuit 170. Then, the decoding circuit 170 converts theextracted serial data S163 a to S163 c into parallel data, then carriesout a decoding process according to the type of the character broadcastindicated by the framing code, and outputs decoded data S170 a to S170 cto the data selection unit 320.

[0167] When the decoded data S170 a to S170 c are inputted to the dataselection unit 320, the error detection circuit 321 detects decodingerrors from the decoded data S170 a to S170 c. Then, the error detectioncircuit 321 outputs a decoded data selection signal S321 a thatindicates decoded data including no decoding error, among the decodeddata S170 a to S170 c. When all of the decoded data S170 a to S170 cinclude decoding errors, the decoded data selection signal S321 aindicating one of these decoded data is outputted. The decoded dataselection circuit 182 selects decoded data including no decoding erroramong the decoded data S170 a to S170 c, in accordance with the decodeddata selection signal S321 a, and outputs the selected data as finaldecoded data S182. The error detection circuit 321 determines whetherthe final decoded data S182 has a decoding error or not, and outputs anerror detection signal S321 b to the amplitude evaluation value settingunit 330 when the final decoded data has a decoding error.

[0168] When the error detection signal S321 b is inputted to theamplitude evaluation value setting unit 330, the error count circuit 331counts decoding errors in a predetermined period, on the basis of theerror detection signal S321 b. When this period expires, the error countcircuit 331 outputs error count data S331 indicating the count ofdecoding errors to the controller 332. The controller 332 detects anoptimum CRI amplitude evaluation value in a case where the number ofdecoding errors is equal to the error count data S331, on the basis ofthe held relationship between the CRI amplitude evaluation value and theerror count data, and outputs an optimum amplitude evaluation value S332to the slice level calculation unit 310. Then, the amplitude evaluationcircuit 312 updates the CRI amplitude evaluation value in accordancewith the optimum amplitude evaluation value S332.

[0169] Next, the method for obtaining the relationship between the CRIamplitude evaluation value and the error count data in the data slicer300, and the method for optimizing the CRI amplitude evaluation valueheld by the amplitude evaluation circuit 312 will be described withreference to a flowchart of FIG. 8.

[0170] This CRI amplitude value optimization process is implemented whena signal shape is unknown, for example at the power-on or at theswitching of receiving channels, to set an optimum CRI amplitudeevaluation value for the signal shape at that time.

[0171] Initially, the controller 332 sets a predetermined start value ofthe CRI amplitude value. More specifically, the controller 332 outputsthe start value as an optimum amplitude evaluation value S332, and theamplitude evaluation circuit 312 sets the CRI amplitude evaluation valueto the optimum amplitude evaluation value S332. In this case, adescription will be given of a case where the retrieval is started fromthe largest value (step S801).

[0172] Then, the slice level calculation unit 310 determines theamplitude, using the CRI amplitude evaluation value that is set in stepS801 as a reference value, then calculates a slice level using the CRIsignal C that is evaluated to have an amplitude of the characterbroadcast, and outputs reference slice level data S311 a, upper slicelevel data S157 a, and lower slice level data S157 b (step S802).

[0173] When the CRI detection period expires and a framing code signal Dis inputted, the data slicing unit 160 binarizes the framing code signalD using the respective slice level data which are calculated in stepS802, and the decoding circuit 170 obtains the framing code. Then, whena text data signal E is inputted, the data slicing unit 160 binarizesthe text data signal E using the respective slice level data which arecalculated in step S802, and the decoding circuit 170 carries out adecoding process for the respective binarized data. The data selectionunit 320 selects decoded data including no decoding error, among thedecoded data S170 a to S170 c, and outputs the selected data as finaldecoded data S182 (step S803).

[0174] When the final decoded data S182 includes a decoding error, theerror detection circuit 321 outputs the error detection signal S321 b,so that the error count circuit 331 counts errors on the basis of theerror detection signal S321 b, and outputs the error count data S331.The controller 332 holds the error count data S331 corresponding to theCRI amplitude evaluation value (optimum amplitude evaluation value S332)at that time (step S804).

[0175] Then, the controller 332 binarizes and decodes the text datasignal E during a predetermined time period that is defined in units ofvertical sync signal, to determine whether the error count data S331 isobtained or not, and the operation returns to step S802 unless theprocessing has been performed during the predetermined time period (stepS805).

[0176] When it is determined in step S805 that the processing has beencarried out during the predetermined time period, the controller 332determines whether the present optimum amplitude evaluation value S332is equal to a predetermined end value or not (step S806).

[0177] When the present optimum amplitude evaluation value S332 is notequal to the end value, the controller 332 subtracts a predeterminedstep value from the present optimum amplitude evaluation value S332.Then, the controller outputs this optimum amplitude evaluation valueS332 to the amplitude evaluation circuit 312. The amplitude evaluationcircuit 312 updates the CRI amplitude evaluation value on the basis ofthe optimum amplitude evaluation value S332. Then, the operation returnsto step S802, and the slice level calculation is performed using the CRIsignal C (step S807).

[0178] On the other hand, when the controller 332 has carried out theprocessing by subtracting the step value from the optimum amplitudeevaluation value S332 up to the end value, the controller 332 selects aCRI amplitude evaluation value that minimizes the number of errors onthe basis of the relationship between the obtained respective CRIamplitude evaluation value and the number of errors (see FIG. 6), andoutputs the selected CRI amplitude evaluation value to the amplitudeevaluation circuit 312 as the optimum amplitude evaluation value S332.The amplitude evaluation circuit 312 updates the CRI amplitudeevaluation value on the basis of the optimum amplitude evaluation valueS332, and finishes the CRI amplitude evaluation value optimizationprocess (step S808).

[0179] As described above, the data slicer 300 according to the thirdembodiment includes the amplitude evaluation circuit 312 that determineswhether the amplitude detection data S311 b calculated by theaverage/amplitude calculation circuit 311 has the amplitude of the CRIsignal C or not, on the basis of the held CRI amplitude evaluationvalues, and the average/amplitude calculation circuit 311 outputs thecalculated average value as reference slice level data S311 a and thecalculated amplitude as amplitude level data S311 c, respectively, onlywhen it is determined that the amplitude detection data S311 b has theamplitude of the CRI signal. Therefore, even when noises of a cycle thatis quite similar to that of the CRI signal C are erroneously detected asthe CRI signal C, the reference slice level data S311 a can becalculated with eliminating the average value calculated on the basis ofthe noises.

[0180] The data slice according to the third embodiment further includesthe slice level offset value calculation circuit 157 that calculates theupper slice level data S157 a by adding the offset value calculated onthe basis of the amplitude level data S311 c to the reference slicelevel data S311 a, and the lower slice level data S157 b by subtractingthe offset value from the reference slice level data S311 a. Therefore,even in cases where the digital video signal S140 is distorted due togroup delay or electric field strength in the transmission system, andbinarized into an erroneous value when the binarization is performedusing only the reference slice level data S311 a, the digital videosignal S140 can be binarized into a correct value using one of the slicelevel data, whereby the occurrence rate of decoding errors can befurther suppressed.

[0181] The data slicer of the third embodiment further includes theerror count circuit 331 that counts decoding errors included in thefinal decoded data S182, and the controller 332 that changes the CRIamplitude evaluation value on the basis of the number of decodingerrors. Therefore, even when the distortion of the digital video signalS140 varies, slice level data that are suitable for the signal shape canbe calculated by updating the CRI amplitude evaluation value adaptivelyto the signal shape, thereby further suppressing the occurrence rate ofdecoding errors.

[0182] In this third embodiment, when the error count data correspondingto each CRI amplitude evaluation value (optimum amplitude evaluationvalue S332) is obtained, the start value of the optimum amplitudeevaluation value S332 is set at the maximum value, and then the stepvalue is successively subtracted from the optimum amplitude evaluationvalue S332, thereby to obtain the error count data S331 corresponding tothe optimum amplitude evaluation value. However, also when the startvalue of the optimumamplitudeevaluationvalueS332 is set at the minimumvalue, and then a step value is successively added to the optimumamplitude evaluation value S332, thereby to obtain the error count dataS331 corresponding to the optimum amplitude evaluation value, the sameeffect as that in the third embodiment can be obtained.

[0183] [Embodiment 4]

[0184] A data slice according to a fourth embodiment of the presentinvention will be described with reference to the drawings.

[0185]FIG. 9 is a block diagram illustrating a construction of a dataslicer 400 according to the fourth embodiment. In FIG. 9, the same orcorresponding elements as those in FIG. 5 are denoted by the samereference numerals.

[0186] As shown in FIG. 9, the data slicer 400 according to the fourthembodiment includes a decoding circuit 420 that outputs decoded dataS420 a to S420 as well as a decoded data detection period gate pulseS420 d while extracted serial data S163 a to S163 c are decoded; and amaximum/minimum retrieval circuit 411 that retrieves the maximum andminimum values of a digital video signal S140 while a CRI detectionrange signal S312 or the decoded data detection period gate pulse S420 dis inputted, and outputs maximum value retrieval data S411 a and minimumvalue retrieval data S411 b. The data slicer 400 further includes aslice level calculation circuit 410 that includes, in addition to thecomponents of the slice level calculation circuit 310 of the thirdembodiment, a decoded data unit pulse generation circuit 412 thatgenerates a decoded data unit pulse S412 at intervals of decoded dataunit on the basis of an extraction pulse S162 that is generated by anextraction pulse generation circuit 162 and the decoded data detectionperiod gate pulse S420 d; and a pulse selection circuit 413 that selectsa frequency evaluation pulse S211 a when the decoded data unit pulseS412 is not generated, while selecting the decoded data unit pulse S412when the decoded data unit pulse S412 is generated, and outputs theselected pulse to an average/amplitude calculation circuit 311.

[0187] Here, the decoded data unit pulse generation circuit 412 countsthe extraction pulse S162 during a period in which the decoded datadetection period gate pulse S420 d is inputted, and generates thedecoded data unit pulse S412 at the intervals of decoded data unit. Forexample, when the decoded data is composed of 8 bits, the decoded dataunit pulse generation circuit 412 counts the extraction pulse S162, andgenerates the decoded data unit pulse S412 at the intervals of 8 bit.

[0188] Next, the operation of the data slicer 400 that is configured asdescribed above will be described.

[0189] When an analog video signal S110 upon which character broadcastserial data are superimposed is inputted through a video signal inputterminal 110, the A/D converter 120 converts the analog video signalinto a digital signal, and outputs the digital video signal S120 to theCRI detection unit 130 and the LPF 140. Then, the LPF 140 eliminatesnoises from the digital video signal S120, and outputs a resultantdigital video signal S140 to the slice level calculation unit 410 andthe data slicing unit 160. The CRI detection unit 130 generates a CRIdetection range signal S132 on the basis of a vertical sync signal S131a and a horizontal sync signal S13 lb which are separated from thedigital video signal S120, and outputs the generated CRI detection rangesignal S132 to the slice level calculation unit 410.

[0190] When the digital video signal 140 and the CRI detection rangesignal S132 are inputted, the slice level calculation unit 410 startscalculation of a slice level. The maximum/minimum retrieval circuit 411retrieves the maximum and minimum values of the digital video signalS140, and outputs maximum value retrieval data S411 a and minimum valueretrieval data S411 b. The falling detection circuit 151 detects thefirst falling and the second falling of the digital video signal S140,and outputs falling detection pulses S151. As the frequency of thedigital video signal S140, which is calculated on the basis of thefalling detection pulses S151, is a frequency corresponding to apredetermined character broadcast system, the frequency evaluationcircuit 153 outputs a frequency evaluation gate pulse S153 to the CRIevaluation circuit 211. The CRI evaluation circuit 211 generates afrequency evaluation pulse S211 a on the basis of the frequencyevaluation gate pulse S153 and the falling detection pulse S151, andoutputs the generated frequency evaluation pulse S211 a to the pulseselection circuit 413. Since a decoded data unit pulse S412 is notinputted to the pulse selection circuit 413 at this time, the pulseselection circuit 413 selects the frequency evaluation pulse S211 a, andoutputs the selected pulse to the maximum/minimum retrieval circuit 411and the maximum/minimum detection circuit 213.

[0191] The maximum/minimum detection circuit 213 samples the maximumvalue retrieval data S411 a and the minimum value retrieval data S411 busing the frequency evaluation pulse S211 a as a load pulse, thereby todetect the maximum and minimum values of the digital video signal S140,and outputs maximum value detection data S213 a and minimum valuedetection data S213 b. Thereafter, the maximum/minimum retrieval circuit411 resets the retrieved data, and retrieves maximum and minimum valuesof the digital video signal S140 that is inputted during a new period.The average/amplitude calculation circuit 311 calculates the amplitudeof the digital video signal S140 on the basis of the maximum valuedetection data S213 a and the minimum value detection data S213 b, andoutputs the calculated amplitude to the amplitude evaluation circuit 312as the amplitude detection data S311 b.

[0192] As the amplitude detection data S311 b has the amplitude of theCRI signal C, the amplitude evaluation circuit 312 outputs an amplitudeevaluation gate pulse S312. The CRI evaluation circuit 211 outputs theamplitude evaluation pulses S211 b that are obtained by extractingpulses of the CRI signal C from the frequency evaluation pulses S211 ain accordance with the amplitude evaluation gate pulse S312, to theaverage/amplitude calculation circuit 311.

[0193] When the amplitude evaluation pulse S211 b is inputted, theaverage/amplitude calculation circuit 311 calculates the amplitude andthe average amplitude of the digital video signal S140 from the maximumvalue detection data S213 a and the minimum value detection data S213 b,and outputs the calculated average amplitude to the data slicing unit160 as reference slice level data S311 a, and the amplitude to the slicelevel offset value calculation circuit 157 as amplitude level data S311c. The slice level offset value calculation circuit 157 calculates anoffset value from the amplitude level data S311 c, and outputs upperslice level data S157 a that is obtained by adding the offset value tothe reference slice level data S311 a and lower slice level data S157 bthat is obtained by subtracting the offset value from the referenceslice level data S311 a.

[0194] When the falling detection circuit 151 detects the next fallingof the CRI signal C and generates the falling detection pulse S151, thesame processing is carried out using the generated falling detectionpulse S151, and the average/amplitude calculation circuit 311 calculatesthe amplitude of the CRI signal and the average amplitude. Then, theaverage/amplitude calculation circuit 311 calculates the average valuebetween the average amplitude of the CRI signal C and the previouslycalculated reference slice level data, and updates the reference slicelevel data S311 a on the basis of the calculated value. Similarly, theaverage/amplitude calculation circuit 311 calculates the average valuebetween the amplitude of the CRI signal C and the previously-calculatedamplitude level data, and updates the amplitude level data S311 c on thebasis of the calculated value. The slice level offset value calculationcircuit 157 calculates an offset value from the amplitude level dataS311 c, and outputs the upper slice level data S157 a and the lowerslice level data S157 b which are obtained by providing the offset tothe reference slice level data S311 a.

[0195] When the digital video signal S140 including a framing codesignal D is inputted to the data slicing unit 160, the binarizationcircuit 161 binarizes the digital video signal S140 using the upperslice level data S157 a, the reference slice level data S311 a, and thelower slice level data S157 b, thereby generating binarized data S161 ato S161 c, respectively. The extraction pulse generation circuit 162generates an extraction pulse S162, and outputs the extraction pulseS162 to the extraction circuit 163 and the decoded data unit pulsegeneration circuit 412. The extraction circuit 163 extracts characterbroadcast serial data from the binarized data S161 a to S161 c inaccordance with the extraction pulse S162, and outputs extracted serialdata S163 a to S163 c. The decoding circuit 420 converts these extractedserial data S163 a to S163 c into parallel data, and detects the framingcode. Further, the decoding circuit 420 outputs the decoded datadetection period gate pulse S420 d to the maximum/minimum retrievalcircuit 411 and the decoded data unit pulse generation circuit 412during a period in which the decoding process is carried out.

[0196] When the decoded data detection period gate pulse S420 d isinputted to the maximum/minimum retrieval circuit 411, themaximum/minimum retrieval circuit 411 retrieves the maximum and minimumvalues of the digital video signal S140, and outputs maximum valueretrieval data S411 a and minimum value retrieval data S411 b.

[0197] On the other hand, when the extraction pulse S162 and the decodeddata detection period gate pulse S420 d are inputted to the decoded dataunit pulse generation circuit 412, the decoded data unit pulsegeneration circuit 412 counts the extraction pulse S162, and outputs adecoded data unit pulse S412 at intervals of data unit. Then, the pulseselection circuit 413 selects the decoded data unit pulse S412, andoutputs the selected pulse to the maximum/minimum detection circuit 213and the maximum/minimum retrieval circuit 411.

[0198] The maximum/minimum detection circuit 213 samples the maximumvalue retrieval data S411 a and the minimum value retrieval data S411 busing the decoded data unit pulse S412 as a load pulse, thereby todetect the maximum and minimum values of the digital video signal S140,and outputs maximum value detection data S213 a and minimum valuedetection data S213 b. Further, when the decoded data unit pulse S412 isinputted to the maximum/minimum retrieval circuit 411, themaximum/minimum retrieval circuit 411 resets the retrieved data, andretrieves maximum and minimum values of the digital video signal S140 ina new period. Then, the average/amplitude calculation circuit 311outputs the average amplitude of the digital video signal S140, which iscalculated from the maximum value detection data S213 a and the minimumvalue detection data S213 b, to the slice level offset value calculationcircuit 157 and the data slicing unit 160 as reference slice level dataS311 a, and the calculated amplitude to the slice level offset valuecalculation circuit 157 as amplitude level data S311 c. The slice leveloffset value calculation circuit 157 calculates an offset value from theamplitude level data S311 c, and outputs upper slice level data S157 athat is obtained by adding the offset value to the reference slice leveldata S311 a and lower slice level data S157 b that is obtained bysubtracting the offset value from the reference slice level data S311 a.

[0199] When the digital video signal S140 including a text data signal Eis inputted to the data slicing unit 160, the binarization circuit 161binarizes the digital video signal S140 using the upper slice level dataS157 a, the reference slice level data S311 a, and the lower slice leveldata S157 b, like in the case including the framing code signal D,thereby to generate binarized data S161 a to S161 c, respectively. Then,the extraction circuit 163 extracts character broadcast serial data fromthe binarized data S161 a to S161 c in accordance with the extractionpulse S162, and outputs extracted serial data S163 a to S163 c. Thedecoding circuit 420 converts the extracted serial data S163 a to S163 cinto parallel data, then performs a decoding process according to thetype of the character broadcast indicated by the framing code, andoutputs decoded data S420 a to S420 c. The decoding circuit 420 furtheroutputs the decoded data detection period gate pulse S420 d to themaximum/minimum retrieval circuit 411 and the decoded data unit pulsegeneration circuit 412 during a period in which the decoding process iscarried out. Then, the decoded data selection circuit 182 selectsdecoded data including no decoding error from among the decoded dataS420 a to S420 c in accordance with the decoded data selection signalS321 a, and outputs the selected data as final decoded data S182. Whendetecting an error in the final decoded data S182, the error detectioncircuit 321 outputs an error detection signal S321 b to the error countcircuit 331. The controller 332 detects an optimum CRI amplitudeevaluation value on the basis of error count data S331 that is obtainedby counting decoding errors in accordance with the error detectionsignal S321 b, and outputs the optimum amplitude evaluation value S332to the slice level calculation unit 410. Then, the amplitude evaluationcircuit 312 updates the CRI amplitude evaluation value in accordancewith the optimum amplitude evaluation value S332.

[0200] On the other hand, when the decoded data detection period gatepulse S420 d is inputted to the maximum/minimum retrieval circuit 411,the maximum/minimum retrieval circuit 411 retrieves the maximum andminimum values of the digital video signal S140 including the text datasignal E, and outputs maximum value retrieval data S411 a and minimumvalue retrieval data S411 b. Further, the pulse selection circuit 413selects the decoded data unit pulse S412 that is outputted from thedecoded data unit pulse generation circuit 412, and outputs the selectedpulse S412 to the maximum/minimum detection circuit 213 and themaximum/minimum retrieval circuit 411. The maximum/minimum detectioncircuit 213 samples the maximum value retrieval data S411 a and theminimum value retrieval data S411 b using the decoded data unit pulseS412 as a load pulse, and outputs maximum value detection data S213 aand minimum value detection data S213 b. The maximum/minimum retrievalcircuit 411 resets the retrieved data in accordance with the decodeddata unit pulse, and retrieves maximum and minimum values of the digitalvideo signal S140 in a new period. The average/amplitude calculationcircuit 311 calculates reference slice level data S311 a and amplitudelevel data S311 c on the basis of the maximum value detection data S213a and the minimum value detection data S213 b. The slice level offsetvalue calculation circuit 157 calculates upper slice level data S157 aand lower slice level data S157 b on the basis of an offset value thatis calculated on the basis of the amplitude level data S311 c.

[0201] Then, the binarization circuit 161 binarizes the digital videosignal S140 using the reference slice level data S311 a, the upper slicelevel data S157 a, and the lower slice level data S157 b which are seton the basis of the digital video signal S140 including the text datasignal E, thereby to generate binarized data S161 a to S161 c,respectively. The extraction circuit 163 extracts character broadcastserial data from the binarized data S161 a to S161 c, and then thedecoding circuit 420 performs a decoding process for extracted serialdata S163 a to S163 c which are outputted from the extraction circuit163 and outputs decoded data S420 a to S420 c. Then, the decoded dataselection circuit 182 selects decoded data including no decoding errorfrom among the decoded data S420 a to S420 c in accordance with thedecoded data selection signal S321 a, and outputs the selected data asfinal decoded data S182. When detecting an error in the final decodeddata S182, the error detection circuit 321 outputs an error detectionsignal S321 b to the error count circuit 331. The controller 332 detectsan optimum CRI amplitude evaluation value on the basis of the errorcount data S331 that is obtained by counting decoding errors by theerror count circuit 331, and outputs an optimum amplitude evaluationvalue S332 to the slice level calculation unit 410. Then, the amplitudeevaluation circuit 312 updates the CRI amplitude evaluation value inaccordance with the optimum amplitude evaluation value S332.

[0202] As described above, according to the data slicer 400 of thefourth embodiment, the maximum/minimum retrieval circuit 411 retrievesnot only the maximum and minimum values of the CRI signal C, but alsothe maximum and minimum values of the framing code signal D and the textdata signal E, thereby to perform the slice level calculation not onlyusing the CRI signal C but also using the framing code signal D and thetext data signal E. Therefore, even when the shapes of signals after theCRI signal would change, slice level data corresponding to therespective signal shapes can be calculated, thereby further suppressingthe occurrence rate of decoding errors.

What is claimed is:
 1. A data slicer comprising: an A/D conversion unitfor converting an input signal including data which are transmitted inserial, into a digital signal; a slice level data calculation unit forcalculating plural pieces of slice level data for binarizing the digitalsignal, on the basis of the digital signal; a binarization unit forbinarizing the digital signal using the plural pieces of slice leveldata, to be converted into plural binarized signals; an extraction pulsegeneration unit for generating an extraction pulse to be used forextracting the data from the binarized signals; an extraction unit forextracting the data from the binarized signals in accordance with theextraction pulse, thereby generating plural pieces of serial data; adecoding unit for decoding the plural pieces of serial data, therebygenerating plural pieces of decoded data; and a decoded data selectionunit for selectively outputting decoded data including no error, fromamong the plural pieces of decoded data.
 2. The data slicer of claim 1wherein the input signal is a signal having a reference waveform of apredetermined cycle, said data slicer includes: a maximum/minimumretrieval unit for retrieving maximum and minimum values of the digitalsignal; and a reference cycle detection unit for determining whether acycle of the digital signal is the cycle of the reference waveform ornot, and said slice level data calculation unit calculates the pluralpieces of the slice level data on the basis of an average value and anamplitude of the digital signal, which are calculated from the maximumand minimum values when the reference waveform cycle is detected.
 3. Thedata slicer of claim 2 wherein the slice level data calculation unitemploys the calculated average value as reference slice level data, andcalculates upper slice level data by adding an offset value that isdecided on the basis of the calculated amplitude, to the reference slicelevel data, and lower slice level data by subtracting the offset valuefrom the reference slice level data.
 4. The data slicer of claim 1wherein the input signal is a signal of character broadcast that istransmitted being superimposed upon a vertical blanking interval of avideo signal.
 5. A data slicer comprising: an A/D conversion unit forconverting an input signal including a reference waveform of apredetermined cycle and amplitude, into a digital signal; a referencecycle detection unit for determining whether a cycle of the digitalsignal is the cycle of the reference waveform or not; a maximum/minimumretrieval unit for retrieving maximum and minimum values of the digitalsignal; an amplitude evaluation unit for determining whether anamplitude of the digital signal, which is calculated from the retrievedmaximum and minimum values, is the amplitude of the reference waveformor not; a slice level data calculation unit that employs an averagevalue of the digital signal, which is calculated from the maximum andminimum values when detecting the cycle and amplitude of the referencewaveform, as slice level data; and a binarization unit for binarizingthe digital signal into the slice level data, to be converted into abinarized signal.
 6. The data slicer of claim 5 wherein themaximum/minimum retrieval unit retrieves maximum and minimum values ofthe digital signal in each cycle, and the amplitude evaluation unitdetermines whether the amplitude calculated from the maximum and minimumvalues in each cycle is the amplitude of the reference waveform or not.7. The data slicer of claim 5 or 6 wherein when calculating the averagevalue from the maximum and minimum values, the slice level calculationunit carries out an averaging process for the calculated average and theslice level data that has been calculated in a previous cycle, andupdates the slice level data on the basis of the obtained average. 8.The data slicer of claim 5 wherein the reference waveform and the datasignal correspond to a signal of character broadcast which istransmitted being superimposed upon a vertical blanking interval of avideo signal.
 9. A data slicer comprising: an A/D conversion unit forconverting an input signal of a predetermined cycle and amplitude,including data which are transmitted in serial, into a digital signal; areference cycle detection unit for determining whether a cycle of thedigital signal is the predetermined cycle or not; a maximum/minimumretrieval unit for retrieving maximum and minimum values of the digitalsignal; an amplitude evaluation unit for determining whether anamplitude of the digital signal, which is calculated from the retrievedmaximum and minimum values, is the predetermined amplitude or not; aslice level data calculation unit for calculating plural pieces of slicelevel data on the basis of an average value and an amplitude of thedigital signal, which are calculated from the maximum and minimum valuesat a time when the predetermined cycle and amplitude are detected; abinarization unit for binarizing the digital signal using the pluralpieces of slice level data, to be converted into plural binarizedsignals; an extraction pulse generation unit for generating anextraction pulse to be used for extracting the data from the binarizedsignals; an extraction unit for extracting the data from the pluralbinarized signals in accordance with the extraction pulse, therebygenerating plural pieces of serial data; a decoding unit for decodingthe plural pieces of serial data, thereby generating plural pieces ofdecoded data; a decoded data selection unit for detecting an error fromthe plural pieces of decoded data, and selectively outputting one of thedecoded data when errors are detected from all of the decoded data, ordecoded data including no error when there are decoded data in which noerror is detected; an error count unit for counting errors in the dataoutputted from the decoded data selection unit; and a controller forcontrolling the evaluation in the amplitude evaluation unit on the basisof the output from the error count unit.
 10. The data slicer of claim 9wherein the input signal includes a reference waveform for calculatingthe slice level data, said data slicer includes a reference waveformdetection unit for detecting the reference waveform, the reference cycledetection unit evaluates the cycle of the digital signal in a periodwhen the reference waveform is detected, the maximum/minimum retrievalunit retrieves the maximum and minimum values of each cycle in theperiod when the reference waveform is detected, and the amplitudeevaluation unit determines whether the amplitude calculated from themaximum and minimum values in each cycle is the predetermined amplitudeor not.
 11. The data slicer of claim 9 wherein the input signal includesa reference waveform for calculating the slice level data, a unit of thedata is composed of predetermined bits; said data slicer includes: areference waveform detection unit for detecting the reference waveform;a data unit detection unit for outputting a data unit detection pulse atintervals of the data unit, on the basis of the decoded data, themaximum/minimum retrieval unit retrieves the maximum and minimum valuesin each cycle in a period when the reference waveform is detected, whileretrieving the maximum and minimum values in each data unit on the basisof the data unit detection pulse in a period when the decoded data areoutputted, and the amplitude evaluation unit determines whether theamplitude calculated from the maximum and minimum values in each cycleor each data unit is the predetermined amplitude or not.
 12. The dataslicer of claim 10 or 11 wherein the slice level data calculation unitemploys the average value as reference slice level data, decides anoffset value on the basis of the amplitude calculated by the amplitudecalculation unit, and calculates upper slice level data by adding theoffset value to the reference slice level data and lower slice leveldata by subtracting the offset value from the reference slice leveldata.
 13. The data slicer of claim 12 wherein when calculating theaverage value from the maximum and minimum values, the slice level datacalculation unit carries out an averaging process for the calculatedaverage value and the reference slice level data that has beencalculated in a previous cycle, and updates the reference slice leveldata on the basis of the obtained average value.
 14. The data slicer ofclaim 12 or 13 wherein when the predetermine cycle and amplitude aredetected, the slice level data calculation unit carries out an averagingprocess for the predetermined amplitude and an amplitude of the previouscycle, and decides the offset value on the basis of the obtained averageamplitude.
 15. The data slicer of claim 9 wherein the input signal is asignal of character broadcast that is transmitted being superimposedupon a vertical blanking interval of a video signal.
 16. A data slicingmethod for binarizing an input signal of a predetermined cycle usingslice level data that are calculated on the basis of the input signal,and extracting data included in the input signal, comprising: an A/Dconversion step of converting the input signal that is transmitted inserial, into a digital signal; a reference cycle detection step ofdetermining whether a cycle of the digital signal is the predeterminedcycle or not; a maximum/minimum retrieval step of retrieving maximum andminimum values of the digital signal; a slice level data calculationstep of calculating plural pieces of slice level data on the basis of anaverage value and an amplitude of the digital signal, which arecalculated from the maximum and minimum values at a time when thepredetermined cycle is detected; a binarization step of converting thedigital signal into plural binarized signals using the plural pieces ofslice level data; a data extraction step of extracting data inaccordance with an extraction pulse for extracting data from thebinarized signals, thereby generating plural pieces of serial data; adecoding step of decoding the plural pieces of serial data, therebygenerating plural pieces of decoded data; and a decoded data selectionstep of determining the presence or absence of errors in the decodeddata, and selectively outputting decoded data including no error.
 17. Adata slicing method for binarizing an input signal of a predeterminedcycle and amplitude using slice level data which are calculated on thebasis of the input signal, and extracting data included in the inputsignal, comprising: an A/D conversion step of converting the inputsignal that is transmitted in serial, into a digital signal; a referencecycle detection step of determining whether a cycle of the digitalsignal is the predetermined cycle or not; a maximum/minimum retrievalstep of retrieving maximum and minimum values of the digital signal; anamplitude evaluation step of determining whether an amplitude of thedigital signal, which is calculated from the retrieved maximum andminimum values is the predetermined amplitude or not; a slice level datacalculation step of calculating plural pieces of slice level data on thebasis of an average value and an amplitude of the digital signal, whichare calculated from the maximum and minimum values at a time when thepredetermined cycle and amplitude are detected; a binarization step ofconverting the digital signal into plural binarized signals using theplural pieces of slice level data; a data extraction step of extractingdata from the plural binarized signals in accordance with an extractionpulse for extracting data, thereby generating plural pieces of serialdata; a decoding step of decoding the plural pieces of serial data,thereby generating plural pieces of decoded data; a decoded dataselection step of detecting errors in the plural pieces of decoded data,and selectively outputting one of the decoded data when errors aredetected from all of the decoded data, or decoded data including noerror when there are decoded data in which no error is detected; and anamplitude evaluation control step of counting errors in the decoded dataselected in the decoded data selection step, and controlling theevaluation in the amplitude evaluation step on the basis of the numberof errors.
 18. The data slicing method of claim 16 or 17 wherein in theslice level data calculation step, the average value is employed asreference slice level data, an offset value is decided on the basis ofthe amplitude, then upper slice level data is calculated by adding theoffset value to the reference slice level data, and lower slice leveldata is calculated by subtracting the offset value from the referenceslice level data.
 19. An amplitude evaluation value setting methodcomprising: a start value setting step of setting a start value at anamplitude evaluation value for determining whether an input signalincluding data which are transmitted in serial is a desired signal ornot; a signal detection step of evaluating an amplitude of the inputsignal on the basis of the amplitude evaluation value in a predeterminedperiod, thereby detecting the desired signal; a slice level datacalculation step of, when detecting the desired signal, calculatingslice level data for binarizing the input signal, on the basis of thedetected desired signal; a binarization step of binarizing the inputsignal using the slice level data, to be converted into a binarizedsignal; a decoding step of decoding serial data which are extracted fromthe binarized signal, thereby generating decoded data; an error countstep of counting errors in the decoded data, and storing the amplitudeevaluation value and the number of errors; an amplitude evaluation valueupdate step of binarizing and decoding the input signal and countingerrors in the decoded data during a predetermined period, thereaftersubjecting the amplitude evaluation value to an arithmetic process usinga predetermined step value, so as to approach an end value, and updatingthe amplitude evaluation value; and an amplitude evaluation valueselection step of selecting an amplitude evaluation value that minimizesthe number of errors as an optimum amplitude evaluation value, on thebasis of the numbers of errors at various amplitude evaluation values,which are obtained by changing the amplitude evaluation value in thepredetermined step value from the start value to the end value.